[PATCH v9 00/19] zswap compression batching

From: Kanchana P Sridhar
Date: Wed Apr 30 2025 - 16:54:04 EST

Compression Batching:
=====================

This patch-series introduces batch compression of pages in large folios to
improve zswap swapout latency. It preserves the existing zswap protocols
for non-batching software compressors by calling crypto_acomp sequentially
per page in the batch. Additionally, in support of hardware accelerators
that can process a batch as an integral unit, the patch-series creates
generic batching interfaces in crypto_acomp, and calls the
crypto_acomp_batch_compress() interface in zswap_compress() for compressors
that intrinsically support batching.

The patch series provides a proof point by using the Intel Analytics
Accelerator (IAA) for implementing the compress/decompress batching API
using hardware parallelism in the iaa_crypto driver and another proof point
with a sequential software compressor, zstd.

SUMMARY:
========

The first proof point is to test with IAA using a sequential call (fully
synchronous, compress one page at a time) vs. a batching call (fully
asynchronous, submit a batch to IAA for parallel compression, then poll for
completion statuses).

The performance testing data with usemem 30 processes and kernel
compilation test using 32 threads, show 67%-77% throughput gains and
28%-32% sys time reduction (usemem30) and 2-3% sys time reduction
(kernel compilation) with zswap_store() large folios using IAA compress
batching as compared to IAA sequential.

The second proof point is to make sure that software algorithms such as
zstd do not regress. The data indicates that for sequential software
algorithms a performance gain is achieved.

With the performance optimizations implemented in patches 18 and 19 of
v9, zstd usemem30 throughput increases by 1%, along with a 6%-8% sys time
reduction. With kernel compilation using zstd, we get a 0.4%-3.2%
reduction in sys time. These optimizations pertain to common code
paths, removing redundant branches/computes, using prefetchw() of the
zswap entry before it is written, and selectively annotating branches
with likely()/unlikely() compiler directives to minimize branch
mis-prediction penalty. Additionally, using the batching code for
non-batching compressors to sequentially compress/store batches of up
to ZSWAP_MAX_BATCH_SIZE (8) pages seems to help, most likely due to
cache locality of working set structures such as the array of
zswap_entry-s for the batch.

Our internal validation of zstd with the batching interface vs. IAA with
the batching interface on Emerald Rapids has shown that IAA
compress/decompress batching gives 21.3% more memory savings as compared
to zstd, for 5% performance loss as compared to the baseline without any
memory pressure. IAA batching demonstrates more than 2X the memory
savings obtained by zstd at this 95% performance KPI.
The compression ratio with IAA is 2.23, and with zstd 2.96. Even with
this compression ratio deficit for IAA, batching is extremely
beneficial. As we improve the compression ratio of the IAA accelerator,
we expect to see even better memory savings with IAA as compared to
software compressors.


Batching Roadmap:
=================

1) Compression batching within large folios (this series).

2) Reclaim batching of hybrid folios:

We can expect to see even more significant performance and throughput
improvements if we use the parallelism offered by IAA to do reclaim
batching of 4K/large folios (really any-order folios), and using the
zswap_store() high throughput compression pipeline to batch-compress
pages comprising these folios, not just batching within large
folios. This is the reclaim batching patch 13 in v1, which we expect
to submit in a separate patch-series.

3) Decompression batching:

We have developed a zswap load batching interface for IAA to be used
for parallel decompression batching, using swapin_readahead().

These capabilities are architected so as to be useful to zswap and
zram. We are actively working on integrating these components with zram.

v9 Performance Summary:
=======================

This is a performance testing summary of results with usemem30
(30 usemem processes running in a cgroup limited at 150G, each trying to
allocate 10G).

usemem30 with 64K folios:
=========================

-----------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-----------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa IAA Batching
vs.
IAA Sequential
-----------------------------------------------------------------------
Total throughput (KB/s) 6,091,607 10,174,344 67%
Avg throughput (KB/s) 203,053 339,144
elapsed time (sec) 100.46 69.70 -31%
sys time (sec) 2,416.97 1,648.37 -32%
-----------------------------------------------------------------------

-----------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-----------------------------------------------------------------------
zswap compressor zstd zstd v9 zstd
improvement
-----------------------------------------------------------------------
Total throughput (KB/s) 6,574,380 6,632,230 1%
Avg throughput (KB/s) 219,146 221,074
elapsed time (sec) 96.58 90.60 -6%
sys time (sec) 2,416.52 2,224.78 -8%
-----------------------------------------------------------------------

usemem30 with 2M folios:
========================

----------------------------------------------------------------------
mm-unstable-4-21-2025 v9
----------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa IAA Batching
vs.
IAA Sequential
----------------------------------------------------------------------
Total throughput (KB/s) 6,371,048 11,282,935 77%
Avg throughput (KB/s) 212,368 376,097
elapsed time (sec) 87.15 63.04 -28%
sys time (sec) 2,011.56 1,450.45 -28%
----------------------------------------------------------------------

----------------------------------------------------------------------
mm-unstable-4-21-2025 v9
----------------------------------------------------------------------
zswap compressor zstd zstd v9 zstd
improvement
----------------------------------------------------------------------
Total throughput (KB/s) 7,320,278 7,428,055 1%
Avg throughput (KB/s) 244,009 247,601
elapsed time (sec) 83.30 81.60 -2%
sys time (sec) 1,970.89 1,857.70 -6%
----------------------------------------------------------------------



DETAILS:
========

(A) From zswap's perspective, the most significant changes are:
===============================================================

1) A unified zswap_compress() API is added to compress multiple
pages:

- If the compressor has multiple acomp requests, i.e., internally
supports batching, crypto_acomp_batch_compress() is called. If all
pages are successfully compressed, the batch is stored in zpool.

- If the compressor can only compress one page at a time, each page
is compressed and stored sequentially.

Many thanks to Yosry for this suggestion, because it is an essential
component of unifying common code paths between sequential/batching
compressions.

prefetchw() is used in zswap_compress() to minimize cache-miss
latency by moving the zswap entry to the cache before it is written
to; reducing sys time by ~1.5% for zstd (non-batching software
compression). In other words, this optimization helps both batching and
software compressors.

Overall, the prefetchw() and likely()/unlikely() annotations prevent
regressions with software compressors like zstd, and generally improve
non-batching compressors' performance with the batching code by ~8%.

2) A new zswap_store_pages() is added, that stores multiple pages in a
folio in a range of indices. This is an extension of the earlier
zswap_store_page(), except it operates on a batch of pages.

3) zswap_store() is modified to store the folio's pages in batches
by calling zswap_store_pages(). If the compressor supports batching,
i.e., has multiple acomp requests, the folio will be compressed in
batches of "pool->nr_reqs". If the compressor has only one acomp
request, the folio will be compressed in batches of
ZSWAP_MAX_BATCH_SIZE pages, where each page in the batch is
compressed sequentially. We see better performance by processing
the folio in batches of ZSWAP_MAX_BATCH_SIZE, due to cache locality
of working set structures such as the array of zswap_entry-s for the
batch.

Many thanks to Yosry and Johannes for steering towards a common
design and code paths for sequential and batched compressions (i.e.,
for software compressors and hardware accelerators such as IAA). As per
Yosry's suggestion in v8, the nr_reqs is an attribute of the
compressor/pool, and hence is stored in struct zswap_pool instead of in
struct crypto_acomp_ctx.

4) Simplifications to the acomp_ctx resources allocation/deletion
vis-a-vis CPU hot[un]plug. This further improves upon v8 of this
patch-series based on the discussion with Yosry, and formalizes the
lifetime of these resources from pool creation to pool
deletion. zswap does not register a CPU hotplug teardown
callback. The acomp_ctx resources will persist through CPU
online/offline transitions. The main changes made to avoid UAF/race
conditions, and correctly handle process migration, are:

a) No acomp_ctx mutex locking in zswap_cpu_comp_prepare().
b) No CPU hotplug teardown callback, no acomp_ctx resources deleted.
c) New acomp_ctx_dealloc() procedure that cleans up the acomp_ctx
resources, and is shared by zswap_cpu_comp_prepare() error
handling and zswap_pool_destroy().
d) The zswap_pool node list instance is removed right after the node
list add function in zswap_pool_create().
e) We directly call mutex_[un]lock(&acomp_ctx->mutex) in
zswap_[de]compress(). acomp_ctx_get_cpu_lock()/acomp_ctx_put_unlock()
are deleted.

The commit log of patch 0015 has a more detailed analysis.


(B) Main changes in crypto_acomp and iaa_crypto:
================================================

1) A new architecture is introduced for IAA device WQs' usage as:
- compress only
- decompress only
- generic, i.e., both compress/decompress.

Further, IAA devices/wqs are assigned to cores based on packages
instead of NUMA nodes.

The WQ rebalancing algorithm that is invoked as WQs are
discovered/deleted has been made very general and flexible so that
the user can control exactly how IAA WQs are used. In addition to the
user being able to specify a WQ type as comp/decomp/generic, the user
can also configure if WQs need to be shared among all same-package
cores, or, whether the cores should be divided up amongst the
available IAA devices.

If distribute_[de]comps is enabled, from a given core's perspective,
the iaa_crypto driver will distribute comp/decomp jobs among all
devices' WQs in round-robin manner. This improves batching latency
and can improve compression/decompression throughput for workloads
that see a lot of swap activity.

The commit log of patch 0006 provides more details on new iaa_crypto
driver parameters added, along with recommended settings.

2) Compress/decompress batching are implemented using
crypto_acomp_batch_[de]compress(), along the lines of v6 since
request chaining is no longer the recommended approach.


(C) The patch-series is organized as follows:
=============================================

1) crypto acomp & iaa_crypto driver enablers for batching: Relevant
patches are tagged with "crypto:" in the subject:

Patches 1-4) Backport some of the crypto patches that revert request
chaining that are in the cryptodev-2.6 git tree and are
yet to be included in mm-unstable. I have also
backported the fix to the scomp off-by-one bug. Further, the
non-request-chaining implementations of
crypto_acomp_[de]compress() are reinstated. Without
patches 1/2/3, the crypto/testmgr issues errors that
prevent deflate-iaa from being used as zswap's
compressor. Once mm-unstable is updated with the
request chaining reverts, patches 1/3/4 can be deleted
from this patch-series.

Patch 5) Reorganizes the iaa_crypto driver code into logically related
sections and avoids forward declarations, in order to facilitate
subsequent iaa_crypto patches. This patch makes no
functional changes.

Patch 6) Makes an infrastructure change in the iaa_crypto driver
to map IAA devices/work-queues to cores based on packages
instead of NUMA nodes. This doesn't impact performance on
the Sapphire Rapids system used for performance
testing. However, this change fixes functional problems we
found on Granite Rapids during internal validation, where the
number of NUMA nodes is greater than the number of packages,
which was resulting in over-utilization of some IAA devices
and non-usage of other IAA devices as per the current NUMA
based mapping infrastructure.

This patch also develops a new architecture that
generalizes how IAA device WQs are used. It enables
designating IAA device WQs as either compress-only or
decompress-only or generic. Once IAA device WQ types are
thus defined, it also allows the configuration of whether
device WQs will be shared by all cores on the package, or
used only by "mapped cores" obtained by a simple allocation
of available IAAs to cores on the package.

As a result of the overhaul of wq_table definition,
allocation and rebalancing, this patch eliminates
duplication of device WQs in per-cpu wq_tables, thereby
saving 140MiB on a 384 cores dual socket Granite Rapids server
with 8 IAAs.

Regardless of how the user has configured the WQs' usage,
the next WQ to use is obtained through a direct look-up in
per-cpu "cpu_comp_wqs" and "cpu_decomp_wqs" structures so
as to minimize latency in the critical path driver compress
and decompress routines.

Patch 7) Defines a "void *data" in struct acomp_req, in response to
Herbert's comments in v8 about avoiding use of
req->base.data. iaa_crypto requires the req->data to
store the idxd_desc allocated in the core
iaa_[de]compress() functions, for later retreival in the
iaa_comp_poll() function to check for the descriptor's
completion status. This async submit-poll is essential for
batching.

Patch 8) Makes a change to iaa_crypto driver's descriptor allocation,
from blocking to non-blocking with retries/timeouts and
mitigations in case of timeouts during compress/decompress
ops. This prevents tasks getting blocked indefinitely, which
was observed when testing 30 cores running workloads, with
only 1 IAA enabled on Sapphire Rapids (out of 4). These
timeouts are typically only encountered, and associated
mitigations exercised, only in configurations with 1 IAA
device shared by 30+ cores.

Patch 9) New CRYPTO_ACOMP_REQ_POLL acomp_req flag to act as a gate for
async poll mode in iaa_crypto.

Patch 10) Adds acomp_alg/crypto_acomp interfaces for get_batch_size(),
batch_compress() and batch_decompress() along with the
corresponding crypto_acomp_batch_size(),
crypto_acomp_batch_compress() and
crypto_acomp_batch_decompress() API for use in zswap.

Patch 11) iaa-crypto driver implementations for the newly added batching
interfaces. iaa_crypto implements the crypto_acomp
get_batch_size() interface that returns an iaa_driver specific
constant, IAA_CRYPTO_MAX_BATCH_SIZE (set to 8U currently).

This patch also provides the iaa_crypto driver implementations
for the batch_compress() and batch_decompress() crypto_acomp
interfaces.

Patch 12) Modifies the default iaa_crypto driver mode to async, now that
iaa_crypto provides a truly async mode that gives
significantly better latency than sync mode for the batching
use case.

Patch 13) Disables verify_compress by default, to facilitate users to
run IAA easily for comparison with software compressors.


2) zswap modifications to enable compress batching in zswap_store()
of large folios (including pmd-mappable folios):

Patch 14) Moves the zswap CPU hotplug procedures under "pool functions",
because they are invoked upon pool creation/deletion.

Patch 15) Simplifies the zswap_pool's per-CPU acomp_ctx resource
management and lifetime to be from pool creation to pool
deletion.

Patch 16) Uses IS_ERR_OR_NULL() in zswap_cpu_comp_prepare() to check for
valid acomp/req, thereby making it consistent with the resource
de-allocation code.

Patch 17) Defines a zswap-specific ZSWAP_MAX_BATCH_SIZE (currently set
as 8U) to denote the maximum number of acomp_ctx batching
resources to allocate, thus limiting the amount of extra
memory used for batching. Further, the "struct
crypto_acomp_ctx" is modified to contain multiple acomp_reqs
and buffers. A new "u8 nr_reqs" member is added to "struct
zswap_pool" to track the number of requests/buffers associated
with the compressor.

Patch 18) Modifies zswap_store() to store the folio in batches of
pool->nr_reqs by calling a new zswap_store_pages() that takes
a range of indices in the folio to be stored.
zswap_store_pages() pre-allocates zswap entries for the batch,
calls zswap_compress() for each page in this range, and stores
the entries in xarray/LRU.

Patch 19) Introduces a new unified implementation of zswap_compress()
for compressors that do and do not support batching. This
eliminates code duplication and facilitates maintainability of
the code with the introduction of compress batching. Further,
there are many optimizations to this common code that result
in workload throughput and performance improvements with
software compressors and hardware accelerators such as IAA.

zstd performance is better or on par with mm-unstable. We
see impressive throughput/performance improvements with IAA
batching vs. no-batching.


With v9 of this patch series, the IAA compress batching feature will be
enabled seamlessly on Intel platforms that have IAA by selecting
'deflate-iaa' as the zswap compressor, and using the iaa_crypto 'async'
sync_mode driver attribute (the default).


System setup for testing:
=========================
Testing of this patch-series was done with mm-unstable as of 4-21-2025,
commit 2c01d9f3c611, without and with this patch-series. Data was
gathered on an Intel Sapphire Rapids (SPR) server, dual-socket 56 cores
per socket, 4 IAA devices per socket, 503 GiB RAM and 525G SSD disk
partition swap. Core frequency was fixed at 2500MHz.

Other kernel configuration parameters:

zswap compressor : zstd, deflate-iaa
zswap allocator : zsmalloc
vm.page-cluster : 0

IAA "compression verification" is disabled and IAA is run in the async
mode (the defaults with this series).

I ran experiments with these workloads:

1) usemem 30 processes with these large folios enabled to "always":
- 64k
- 2048k

IAA WQ Configuration:

Since usemem sees practically no swapin activity, we set up 1 WQ per
IAA device, so that all 128 entries are available for compress
jobs. All IAA's WQs are available to all package cores to send
compress/decompress jobs in a round-robin manner.

4 IAA devices
1 WQ per device
echo 0 > /sys/bus/dsa/drivers/crypto/g_comp_wqs_per_iaa
echo 1 > /sys/bus/dsa/drivers/crypto/distribute_comps
echo 1 > /sys/bus/dsa/drivers/crypto/distribute_decomps

2) Kernel compilation allmodconfig with 2G max memory, 32 threads, with
these large folios enabled to "always":
- 64k

IAA WQ Configuration:

Since kernel compilation sees considerable swapin activity, we set up
2 WQs per IAA device, each containing 64 entries. The driver sends
decompresses to wqX.0 and compresses to wqX.1. All IAAs' wqX.0 are
available to all package cores to send decompress jobs in a
round-robin manner. Likewise, all IAAs' wqX.1 are available to all
package cores to send decompress jobs in a round-robin manner.

4 IAA devices
2 WQs per device
echo 1 > /sys/bus/dsa/drivers/crypto/g_comp_wqs_per_iaa
echo 1 > /sys/bus/dsa/drivers/crypto/distribute_comps
echo 1 > /sys/bus/dsa/drivers/crypto/distribute_decomps


Performance testing (usemem30):
===============================
The vm-scalability "usemem" test was run in a cgroup whose memory.high
was fixed at 150G. The is no swap limit set for the cgroup. 30 usemem
processes were run, each allocating and writing 10G of memory, and sleeping
for 10 sec before exiting:

usemem --init-time -w -O -b 1 -s 10 -n 30 10g


64K folios: usemem30: deflate-iaa:
==================================

-------------------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-------------------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa IAA Batching
vs.
IAA Sequential
-------------------------------------------------------------------------------
Total throughput (KB/s) 6,091,607 10,174,344 67%
Avg throughput (KB/s) 203,053 339,144
elapsed time (sec) 100.46 69.70 -31%
sys time (sec) 2,416.97 1,648.37 -32%

-------------------------------------------------------------------------------
memcg_high 1,262,996 1,403,680
memcg_swap_fail 2,712 2,105
zswpout 58,146,954 64,508,450
zswpin 91 256
pswpout 0 0
pswpin 0 0
thp_swpout 0 0
thp_swpout_fallback 0 0
64kB_swpout_fallback 2,712 2,105
pgmajfault 2,858 3,032
ZSWPOUT-64kB 3,631,559 4,029,802
SWPOUT-64kB 0 0
-------------------------------------------------------------------------------


2M folios: usemem30: deflate-iaa:
=================================

-------------------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-------------------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa IAA Batching
vs.
IAA Sequential
-------------------------------------------------------------------------------
Total throughput (KB/s) 6,371,048 11,282,935 77%
Avg throughput (KB/s) 212,368 376,097
elapsed time (sec) 87.15 63.04 -28%
sys time (sec) 2,011.56 1,450.45 -28%

-------------------------------------------------------------------------------
memcg_high 116,156 125,138
memcg_swap_fail 348 248
zswpout 59,815,486 64,509,928
zswpin 442 422
pswpout 0 0
pswpin 0 0
thp_swpout 0 0
thp_swpout_fallback 348 248
pgmajfault 3,575 3,272
ZSWPOUT-2048kB 116,480 125,759
SWPOUT-2048kB 0 0
-------------------------------------------------------------------------------


64K folios: usemem30: zstd:
===========================

-------------------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-------------------------------------------------------------------------------
zswap compressor zstd zstd v9 zstd
improvement
-------------------------------------------------------------------------------
Total throughput (KB/s) 6,574,380 6,632,230 1%
Avg throughput (KB/s) 219,146 221,074
elapsed time (sec) 96.58 90.60 -6%
sys time (sec) 2,416.52 2,224.78 -8%

-------------------------------------------------------------------------------
memcg_high 1,117,577 1,110,504
memcg_swap_fail 65 2,217
zswpout 48,771,672 48,806,988
zswpin 137 429
pswpout 0 0
pswpin 0 0
thp_swpout 0 0
thp_swpout_fallback 0 0
64kB_swpout_fallback 65 2,217
pgmajfault 3,286 3,224
ZSWPOUT-64kB 3,048,122 3,048,198
SWPOUT-64kB 0 0
-------------------------------------------------------------------------------


2M folios: usemem30: zstd:
==========================

-------------------------------------------------------------------------------
mm-unstable-4-21-2025 v9
-------------------------------------------------------------------------------
zswap compressor zstd zstd v9 zstd
improvement
-------------------------------------------------------------------------------
Total throughput (KB/s) 7,320,278 7,428,055 1%
Avg throughput (KB/s) 244,009 247,601
elapsed time (sec) 83.30 81.60 -2%
sys time (sec) 1,970.89 1,857.70 -6%

-------------------------------------------------------------------------------
memcg_high 92,970 92,708
memcg_swap_fail 59 172
zswpout 48,043,615 47,896,223
zswpin 77 416
pswpout 0 0
pswpin 0 0
thp_swpout 0 0
thp_swpout_fallback 59 172
pgmajfault 2,815 3,170
ZSWPOUT-2048kB 93,776 93,381
SWPOUT-2048kB 0 0
-------------------------------------------------------------------------------



Performance testing (Kernel compilation, allmodconfig):
=======================================================

The experiments with kernel compilation test use 32 threads and build
the "allmodconfig" that takes ~14 minutes, and has considerable
swapout/swapin activity. The cgroup's memory.max is set to 2G.


64K folios: Kernel compilation/allmodconfig:
============================================

-------------------------------------------------------------------------------
mm-unstable v9 mm-unstable v9
-------------------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa zstd zstd
-------------------------------------------------------------------------------
real_sec 835.31 837.75 858.73 852.22
user_sec 15,649.58 15,660.48 15,682.66 15,649.91
sys_sec 3,705.03 3,642.59 4,858.46 4,703.58
-------------------------------------------------------------------------------
Max_Res_Set_Size_KB 1,874,524 1,872,200 1,871,248 1,870,972
-------------------------------------------------------------------------------
memcg_high 0 0 0 0
memcg_swap_fail 0 0 0 0
zswpout 89,767,776 91,376,740 76,444,847 73,771,346
zswpin 26,362,204 27,700,717 22,138,662 21,287,433
pswpout 360 574 52 154
pswpin 275 551 19 63
thp_swpout 0 0 0 0
thp_swpout_fallback 0 0 0 0
64kB_swpout_fallback 0 1,523 0 0
pgmajfault 27,938,009 29,559,339 23,339,818 22,458,108
ZSWPOUT-64kB 2,958,806 2,992,126 2,444,259 2,382,986
SWPOUT-64kB 21 30 3 8
-------------------------------------------------------------------------------


2M folios: Kernel compilation/allmodconfig:
===========================================

-------------------------------------------------------------------------------
mm-unstable v9 mm-unstable v9
-------------------------------------------------------------------------------
zswap compressor deflate-iaa deflate-iaa zstd zstd
-------------------------------------------------------------------------------
real_sec 790.66 789.01 818.46 819.08
user_sec 15,757.60 15,759.57 15,785.34 15,777.70
sys_sec 4,307.92 4,184.09 5,602.95 5,582.45
-------------------------------------------------------------------------------
Max_Res_Set_Size_KB 1,871,100 1,872,892 1,872,892 1,872,888
-------------------------------------------------------------------------------
memcg_high 0 0 0 0
memcg_swap_fail 0 0 0 0
zswpout 107,349,845 101,481,140 90,083,661 90,818,923
zswpin 37,486,883 35,081,184 29,823,462 29,597,292
pswpout 3,664 1,191 1,066 1,617
pswpin 1,594 138 37 1,594
thp_swpout 7 2 2 3
thp_swpout_fallback 9,434 8,100 6,354 5,809
pgmajfault 38,781,821 36,235,171 30,677,937 30,442,685
ZSWPOUT-2048kB 8,810 7,772 7,857 8,515
-------------------------------------------------------------------------------


With the iaa_crypto driver changes for non-blocking descriptor allocations,
no timeouts-with-mitigations were seen in compress/decompress jobs, for all
of the above experiments.



Changes since v8:
=================
1) Rebased to mm-unstable as of 4-21-2025, commit 2c01d9f3c611.
2) Backported commits for reverting request chaining, since these are
in cryptodev-2.6 but not yet in mm-unstable: without these backports,
deflate-iaa is non-functional in mm-unstable:
commit 64929fe8c0a4 ("crypto: acomp - Remove request chaining")
commit 5976fe19e240 ("Revert "crypto: testmgr - Add multibuffer acomp
testing"")
Backported this hotfix as well:
commit 002ba346e3d7 ("crypto: scomp - Fix off-by-one bug when
calculating last page").
3) crypto_acomp_[de]compress() restored to non-request chained
implementations since request chaining has been removed from acomp in
commit 64929fe8c0a4 ("crypto: acomp - Remove request chaining").
4) New IAA WQ architecture to denote WQ type and whether or not a WQ
should be shared among all package cores, or only to the "mapped"
ones from an even cores-to-IAA distribution scheme.
5) Compress/decompress batching are implemented in iaa_crypto using new
crypto_acomp_batch_compress()/crypto_acomp_batch_decompress() API.
6) Defines a "void *data" in struct acomp_req, based on Herbert advising
against using req->base.data in the driver. This is needed for async
submit-poll to work.
7) In zswap.c, moved the CPU hotplug callbacks to reside in "pool
functions", per Yosry's suggestion to move procedures in a distinct
patch before refactoring patches.
8) A new "u8 nr_reqs" member is added to "struct zswap_pool" to track
the number of requests/buffers associated with the per-cpu acomp_ctx,
as per Yosry's suggestion.
9) Simplifications to the acomp_ctx resources allocation, deletion,
locking, and for these to exist from pool creation to pool deletion,
based on v8 code review discussions with Yosry.
10) Use IS_ERR_OR_NULL() consistently in zswap_cpu_comp_prepare() and
acomp_ctx_dealloc(), as per Yosry's v8 comment.
11) zswap_store_folio() is deleted, and instead, the loop over
zswap_store_pages() is moved inline in zswap_store(), per Yosry's
suggestion.
12) Better structure in zswap_compress(), unified procedure that
compresses/stores a batch of pages for both, non-batching and
batching compressors. Renamed from zswap_batch_compress() to
zswap_compress(): Thanks Yosry for these suggestions.


Changes since v7:
=================
1) Rebased to mm-unstable as of 3-3-2025, commit 5f089a9aa987.
2) Changed the acomp_ctx->nr_reqs to be u8 since ZSWAP_MAX_BATCH_SIZE is
defined as 8U, for saving memory in this per-cpu structure.
3) Fixed a typo in code comments in acomp_ctx_get_cpu_lock():
acomp_ctx->initialized to acomp_ctx->__online.
4) Incorporated suggestions from Yosry, Chengming, Nhat and Johannes,
thanks to all!
a) zswap_batch_compress() replaces zswap_compress(). Thanks Yosry
for this suggestion!
b) Process the folio in sub-batches of ZSWAP_MAX_BATCH_SIZE, regardless
of whether or not the compressor supports batching. This gets rid of
the kmalloc(entries), and allows us to allocate an array of
ZSWAP_MAX_BATCH_SIZE entries on the stack. This is implemented in
zswap_store_pages().
c) Use of a common structure and code paths for compressing a folio in
batches, either as a request chain (in parallel in IAA hardware) or
sequentially. No code duplication since zswap_compress() has been
replaced with zswap_batch_compress(), simplifying maintainability.
5) A key difference between compressors that support batching and
those that do not, is that for the latter, the acomp_ctx mutex is
locked/unlocked per ZSWAP_MAX_BATCH_SIZE batch, so that decompressions
to handle page-faults can make progress. This fixes the zstd kernel
compilation regression seen in v7. For compressors that support
batching, for e.g. IAA, the mutex is locked/released once for storing
the folio.
6) Used likely/unlikely compiler directives and prefetchw to restore
performance with the common code paths.

Changes since v6:
=================
1) Rebased to mm-unstable as of 2-27-2025, commit d58172d128ac.

2) Deleted crypto_acomp_batch_compress() and
crypto_acomp_batch_decompress() interfaces, as per Herbert's
suggestion. Batching is instead enabled by chaining the requests. For
non-batching compressors, there is no request chaining involved. Both,
batching and non-batching compressions are accomplished by zswap by
calling:

crypto_wait_req(crypto_acomp_compress(acomp_ctx->reqs[0]), &acomp_ctx->wait);

3) iaa_crypto implementation of batch compressions/decompressions using
request chaining, as per Herbert's suggestions.
4) Simplification of the acomp_ctx resource allocation/deletion with
respect to CPU hot[un]plug, to address Yosry's suggestions to explore the
mutex options in zswap_cpu_comp_prepare(). Yosry, please let me know if
the per-cpu memory cost of this proposed change is acceptable (IAA:
64.8KB, Software compressors: 8.2KB). On the positive side, I believe
restarting reclaim on a CPU after it has been through an offline-online
transition, will be much faster by not deleting the acomp_ctx resources
when the CPU gets offlined.
5) Use of lockdep assertions rather than comments for internal locking
rules, as per Yosry's suggestion.
6) No specific references to IAA in zswap.c, as suggested by Yosry.
7) Explored various solutions other than the v6 zswap_store_folio()
implementation, to fix the zstd regression seen in v5, to attempt to
unify common code paths, and to allocate smaller arrays for the zswap
entries on the stack. All these options were found to cause usemem30
latency regression with zstd. The v6 version of zswap_store_folio() is
the only implementation that does not cause zstd regression, confirmed
by 10 consecutive runs, each giving quite consistent latency
numbers. Hence, the v6 implementation is carried forward to v7, with
changes for branching for batching vs. sequential compression API
calls.


Changes since v5:
=================
1) Rebased to mm-unstable as of 2-1-2025, commit 7de6fd8ab650.

Several improvements, regression fixes and bug fixes, based on Yosry's
v5 comments (Thanks Yosry!):

2) Fix for zstd performance regression in v5.
3) Performance debug and fix for marginal improvements with IAA batching
vs. sequential.
4) Performance testing data compares IAA with and without batching, instead
of IAA batching against zstd.
5) Commit logs/zswap comments not mentioning crypto_acomp implementation
details.
6) Delete the pr_info_once() when batching resources are allocated in
zswap_cpu_comp_prepare().
7) Use kcalloc_node() for the multiple acomp_ctx buffers/reqs in
zswap_cpu_comp_prepare().
8) Simplify and consolidate error handling cleanup code in
zswap_cpu_comp_prepare().
9) Introduce zswap_compress_folio() in a separate patch.
10) Bug fix in zswap_store_folio() when xa_store() failure can cause all
compressed objects and entries to be freed, and UAF when zswap_store()
tries to free the entries that were already added to the xarray prior
to the failure.
11) Deleting compressed_bytes/bytes. zswap_store_folio() also comprehends
the recent fixes in commit bf5eaaaf7941 ("mm/zswap: fix inconsistency
when zswap_store_page() fails") by Hyeonggon Yoo.

iaa_crypto improvements/fixes/changes:

12) Enables asynchronous mode and makes it the default. With commit
4ebd9a5ca478 ("crypto: iaa - Fix IAA disabling that occurs when
sync_mode is set to 'async'"), async mode was previously just sync. We
now have true async support.
13) Change idxd descriptor allocations from blocking to non-blocking with
timeouts, and mitigations for compress/decompress ops that fail to
obtain a descriptor. This is a fix for tasks blocked errors seen in
configurations where 30+ cores are running workloads under high memory
pressure, and sending comps/decomps to 1 IAA device.
14) Fixes a bug with unprotected access of "deflate_generic_tfm" in
deflate_generic_decompress(), which can cause data corruption and
zswap_decompress() kernel crash.
15) zswap uses crypto_acomp_batch_compress() with async polling instead of
request chaining for slightly better latency. However, the request
chaining framework itself is unchanged, preserved from v5.


Changes since v4:
=================
1) Rebased to mm-unstable as of 12-20-2024, commit 5555a83c82d6.
2) Added acomp request chaining, as suggested by Herbert. Thanks Herbert!
3) Implemented IAA compress batching using request chaining.
4) zswap_store() batching simplifications suggested by Chengming, Yosry and
Nhat, thanks to all!
- New zswap_compress_folio() that is called by zswap_store().
- Move the loop over folio's pages out of zswap_store() and into a
zswap_store_folio() that stores all pages.
- Allocate all zswap entries for the folio upfront.
- Added zswap_batch_compress().
- Branch to call zswap_compress() or zswap_batch_compress() inside
zswap_compress_folio().
- All iterations over pages kept in same function level.
- No helpers other than the newly added zswap_store_folio() and
zswap_compress_folio().


Changes since v3:
=================
1) Rebased to mm-unstable as of 11-18-2024, commit 5a7056135bb6.
2) Major re-write of iaa_crypto driver's mapping of IAA devices to cores,
based on packages instead of NUMA nodes.
3) Added acomp_has_async_batching() API to crypto acomp, that allows
zswap/zram to query if a crypto_acomp has registered batch_compress and
batch_decompress interfaces.
4) Clear the poll bits on the acomp_reqs passed to
iaa_comp_a[de]compress_batch() so that a module like zswap can be
confident about the acomp_reqs[0] not having the poll bit set before
calling the fully synchronous API crypto_acomp_[de]compress().
Herbert, I would appreciate it if you can review changes 2-4; in patches
1-8 in v4. I did not want to introduce too many iaa_crypto changes in
v4, given that patch 7 is already making a major change. I plan to work
on incorporating the request chaining using the ahash interface in v5
(I need to understand the basic crypto ahash better). Thanks Herbert!
5) Incorporated Johannes' suggestion to not have a sysctl to enable
compress batching.
6) Incorporated Yosry's suggestion to allocate batching resources in the
cpu hotplug onlining code, since there is no longer a sysctl to control
batching. Thanks Yosry!
7) Incorporated Johannes' suggestions related to making the overall
sequence of events between zswap_store() and zswap_batch_store() similar
as much as possible for readability and control flow, better naming of
procedures, avoiding forward declarations, not inlining error path
procedures, deleting zswap internal details from zswap.h, etc. Thanks
Johannes, really appreciate the direction!
I have tried to explain the minimal future-proofing in terms of the
zswap_batch_store() signature and the definition of "struct
zswap_batch_store_sub_batch" in the comments for this struct. I hope the
new code explains the control flow a bit better.


Changes since v2:
=================
1) Rebased to mm-unstable as of 11-5-2024, commit 7994b7ea6ac8.
2) Fixed an issue in zswap_create_acomp_ctx() with checking for NULL
returned by kmalloc_node() for acomp_ctx->buffers and for
acomp_ctx->reqs.
3) Fixed a bug in zswap_pool_can_batch() for returning true if
pool->can_batch_comp is found to be equal to BATCH_COMP_ENABLED, and if
the per-cpu acomp_batch_ctx tests true for batching resources having
been allocated on this cpu. Also, changed from per_cpu_ptr() to
raw_cpu_ptr().
4) Incorporated the zswap_store_propagate_errors() compilation warning fix
suggested by Dan Carpenter. Thanks Dan!
5) Replaced the references to SWAP_CRYPTO_SUB_BATCH_SIZE in comments in
zswap.h, with SWAP_CRYPTO_BATCH_SIZE.

Changes since v1:
=================
1) Rebased to mm-unstable as of 11-1-2024, commit 5c4cf96cd702.
2) Incorporated Herbert's suggestions to use an acomp_req flag to indicate
async/poll mode, and to encapsulate the polling functionality in the
iaa_crypto driver. Thanks Herbert!
3) Incorporated Herbert's and Yosry's suggestions to implement the batching
API in iaa_crypto and to make its use seamless from zswap's
perspective. Thanks Herbert and Yosry!
4) Incorporated Yosry's suggestion to make it more convenient for the user
to enable compress batching, while minimizing the memory footprint
cost. Thanks Yosry!
5) Incorporated Yosry's suggestion to de-couple the shrink_folio_list()
reclaim batching patch from this series, since it requires a broader
discussion.


I would greatly appreciate code review comments for the iaa_crypto driver
and mm patches included in this series!

Thanks,
Kanchana



Kanchana P Sridhar (19):
crypto: acomp - Remove request chaining
crypto: acomp - Reinstate non-chained crypto_acomp_[de]compress().
Revert "crypto: testmgr - Add multibuffer acomp testing"
crypto: scomp - Fix off-by-one bug when calculating last page
crypto: iaa - Re-organize the iaa_crypto driver code.
crypto: iaa - New architecture for IAA device WQ comp/decomp usage &
core mapping.
crypto: iaa - Define and use req->data instead of req->base.data.
crypto: iaa - Descriptor allocation timeouts with mitigations in
iaa_crypto.
crypto: iaa - CRYPTO_ACOMP_REQ_POLL acomp_req flag for sequential vs.
parallel.
crypto: acomp - New interfaces to facilitate batching support in acomp
& drivers.
crypto: iaa - Implement crypto_acomp batching interfaces for Intel
IAA.
crypto: iaa - Enable async mode and make it the default.
crypto: iaa - Disable iaa_verify_compress by default.
mm: zswap: Move the CPU hotplug procedures under "pool functions".
mm: zswap: Per-CPU acomp_ctx resources exist from pool creation to
deletion.
mm: zswap: Consistently use IS_ERR_OR_NULL() to check acomp_ctx
resources.
mm: zswap: Allocate pool batching resources if the compressor supports
batching.
mm: zswap: zswap_store() will process a folio in batches.
mm: zswap: Batched zswap_compress() with compress batching of large
folios.

.../driver-api/crypto/iaa/iaa-crypto.rst | 145 +-
crypto/acompress.c | 112 +-
crypto/scompress.c | 28 +-
crypto/testmgr.c | 147 +-
drivers/crypto/intel/iaa/iaa_crypto.h | 30 +-
drivers/crypto/intel/iaa/iaa_crypto_main.c | 1934 ++++++++++++-----
include/crypto/acompress.h | 129 +-
include/crypto/internal/acompress.h | 25 +-
mm/zswap.c | 684 +++---
9 files changed, 2199 insertions(+), 1035 deletions(-)


base-commit: 2c01d9f3c61101355afde90dc5c0b39d9a772ef3
--
2.27.0