Re: [PATCH mm-unstable v5 01/10] mm: add folio dtor and order setter functions

From: David Hildenbrand
Date: Mon Dec 12 2022 - 13:35:37 EST

On 07.12.22 05:11, Muchun Song wrote:


On Dec 7, 2022, at 11:42, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:

On 12/07/22 11:34, Muchun Song wrote:


On Nov 30, 2022, at 06:50, Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx> wrote:

Add folio equivalents for set_compound_order() and set_compound_page_dtor().

Also remove extra new-lines introduced by mm/hugetlb: convert
move_hugetlb_state() to folios and mm/hugetlb_cgroup: convert
hugetlb_cgroup_uncharge_page() to folios.

Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Suggested-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
---
include/linux/mm.h | 16 ++++++++++++++++
mm/hugetlb.c | 4 +---
2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a48c5ad16a5e..2bdef8a5298a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -972,6 +972,13 @@ static inline void set_compound_page_dtor(struct page *page,
page[1].compound_dtor = compound_dtor;
}

+static inline void folio_set_compound_dtor(struct folio *folio,
+ enum compound_dtor_id compound_dtor)
+{
+ VM_BUG_ON_FOLIO(compound_dtor >= NR_COMPOUND_DTORS, folio);
+ folio->_folio_dtor = compound_dtor;
+}
+
void destroy_large_folio(struct folio *folio);

static inline int head_compound_pincount(struct page *head)
@@ -987,6 +994,15 @@ static inline void set_compound_order(struct page *page, unsigned int order)
#endif
}

+static inline void folio_set_compound_order(struct folio *folio,
+ unsigned int order)
+{
+ folio->_folio_order = order;
+#ifdef CONFIG_64BIT
+ folio->_folio_nr_pages = order ? 1U << order : 0;

It seems that you think the user could pass 0 to order. However,
->_folio_nr_pages and ->_folio_order fields are invalid for order-0 pages.
You should not touch it. So this should be:

static inline void folio_set_compound_order(struct folio *folio,
unsigned int order)
{
if (!folio_test_large(folio))
return;

folio->_folio_order = order;
#ifdef CONFIG_64BIT
folio->_folio_nr_pages = 1U << order;
#endif
}

I believe this was changed to accommodate the code in
__destroy_compound_gigantic_page(). It is used in a subsequent patch.
Here is the v6.0 version of the routine.

Thanks for your clarification.


static void __destroy_compound_gigantic_page(struct page *page,
unsigned int order, bool demote)
{
int i;
int nr_pages = 1 << order;
struct page *p = page + 1;

atomic_set(compound_mapcount_ptr(page), 0);
atomic_set(compound_pincount_ptr(page), 0);

for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
p->mapping = NULL;
clear_compound_head(p);
if (!demote)
set_page_refcounted(p);
}

set_compound_order(page, 0);
#ifdef CONFIG_64BIT
page[1].compound_nr = 0;
#endif
__ClearPageHead(page);
}


Might have been better to change this set_compound_order call to
folio_set_compound_order in this patch.


Agree. It has confused me a lot. I suggest changing the code to the
followings. The folio_test_large() check is still to avoid unexpected
users for OOB.

static inline void folio_set_compound_order(struct folio *folio,
unsigned int order)
{
VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
// or
// if (!folio_test_large(folio))
// return;

folio->_folio_order = order;
#ifdef CONFIG_64BIT
folio->_folio_nr_pages = order ? 1U << order : 0;
#endif
}

Thanks.

On mm-stable, dynamically allocating gigantic pages gives me:

[ 23.625105] page:00000000ae27bd2a refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1800
[ 23.635117] flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
[ 23.641969] raw: 0017fffc00000000 ffffa4edc489bb58 fffff784c6000048 0000000000000000
[ 23.650141] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[ 23.657907] page dumped because: VM_BUG_ON_FOLIO(!folio_test_large(folio))
[ 23.663955] ------------[ cut here ]------------
[ 23.667680] kernel BUG at include/linux/mm.h:1030!
[ 23.673378] invalid opcode: 0000 [#1] PREEMPT SMP PTI
[ 23.681610] CPU: 3 PID: 1220 Comm: bash Not tainted 6.1.0-rc4+ #13
[ 23.690281] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-1.fc36 04/01/2014
[ 23.699837] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
[ 23.706587] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 83 e8 09
[ 23.725954] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
[ 23.731001] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 0000000000000000
[ 23.736065] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 00000000ffffffff
[ 23.740866] RBP: 0000000000040000 R08: 0000000000000000 R09: ffffa4edc489bb58
[ 23.745385] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: fffff784c6000000
[ 23.749464] R13: 0000000000040000 R14: fffff784c6000000 R15: ffff9266039fb900
[ 23.753176] FS: 00007f69a9703740(0000) GS:ffff92696f8c0000(0000) knlGS:0000000000000000
[ 23.758299] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 23.761275] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 0000000000770ee0
[ 23.764929] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 23.768572] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 23.772221] PKRU: 55555554
[ 23.773696] Call Trace:
[ 23.776170] <TASK>
[ 23.777258] alloc_fresh_hugetlb_folio+0x14b/0x220
[ 23.779406] alloc_pool_huge_page+0x7c/0x110
[ 23.781273] __nr_hugepages_store_common+0x191/0x400
[ 23.783369] ? __mod_memcg_lruvec_state+0x93/0x110
[ 23.785343] ? __mod_lruvec_page_state+0xa6/0x1a0
[ 23.787223] ? _copy_from_iter+0x8c/0x540
[ 23.788788] ? __kmem_cache_alloc_node+0x13b/0x2a0
[ 23.790577] ? kernfs_fop_write_iter+0x174/0x1f0
[ 23.792313] nr_hugepages_store+0x57/0x70
[ 23.793754] kernfs_fop_write_iter+0x11b/0x1f0
[ 23.795337] vfs_write+0x1e1/0x3a0
[ 23.796531] ksys_write+0x53/0xd0
[ 23.797690] do_syscall_64+0x37/0x90
[ 23.798947] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 23.800602] RIP: 0033:0x7f69a9501977
[ 23.801798] Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 14
[ 23.807322] RSP: 002b:00007ffce87f3338 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 23.809460] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f69a9501977
[ 23.811485] RDX: 0000000000000002 RSI: 00005652a970e5e0 RDI: 0000000000000001
[ 23.813443] RBP: 00005652a970e5e0 R08: 0000000000000000 R09: 0000000000000073
[ 23.815385] R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000002
[ 23.817289] R13: 00007f69a95f9780 R14: 0000000000000002 R15: 00007f69a95f49e0
[ 23.819176] </TASK>
[ 23.819792] Modules linked in: intel_rapl_msr intel_rapl_common intel_uncore_frequency_common isst_ir
[ 23.829056] ---[ end trace 0000000000000000 ]---
[ 23.830413] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
[ 23.832390] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 83 e8 09
[ 23.836787] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
[ 23.838083] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 0000000000000000
[ 23.839764] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 00000000ffffffff
[ 23.841456] RBP: 0000000000040000 R08: 0000000000000000 R09: ffffa4edc489bb58
[ 23.843150] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: fffff784c6000000
[ 23.844836] R13: 0000000000040000 R14: fffff784c6000000 R15: ffff9266039fb900
[ 23.846521] FS: 00007f69a9703740(0000) GS:ffff92696f8c0000(0000) knlGS:0000000000000000
[ 23.848417] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 23.849797] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 0000000000770ee0
[ 23.851491] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 23.853181] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 23.854861] PKRU: 55555554


Something's broken.

--
Thanks,

David / dhildenb