[RFC PATCH v4 13/13] hugetlbfs: parallelize hugetlbfs_fallocate with ktask

From: Daniel Jordan
Date: Mon Nov 05 2018 - 11:58:04 EST

hugetlbfs_fallocate preallocates huge pages to back a file in a
hugetlbfs filesystem. The time to call this function grows linearly
with size.

ktask performs well with its default thread count of 4; higher thread
counts are given for context only.

Machine: Intel(R) Xeon(R) CPU E7-8895 v3 @ 2.60GHz, 288 CPUs, 1T memory
Test: fallocate(1) a file on a hugetlbfs filesystem

nthread speedup size (GiB) min time (s) stdev
1 200 127.53 2.19
2 3.09x 200 41.30 2.11
4 5.72x 200 22.29 0.51
8 9.45x 200 13.50 2.58
16 9.74x 200 13.09 1.64

1 400 193.09 2.47
2 2.14x 400 90.31 3.39
4 3.84x 400 50.32 0.44
8 5.11x 400 37.75 1.23
16 6.12x 400 31.54 3.13

The primary bottleneck for better scaling at higher thread counts is
hugetlb_fault_mutex_table[hash]. perf showed L1-dcache-loads increase
with 8 threads and again sharply with 16 threads, and a CPU counter
profile showed that 31% of the L1d misses were on
hugetlb_fault_mutex_table[hash] in the 16-thread case.

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 114 +++++++++++++++++++++++++++++++++++--------
1 file changed, 93 insertions(+), 21 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 762028994f47..a73548a96061 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -37,6 +37,7 @@
#include <linux/magic.h>
#include <linux/migrate.h>
#include <linux/uio.h>
+#include <linux/ktask.h>

#include <linux/uaccess.h>

@@ -104,11 +105,16 @@ static const struct fs_parameter_description hugetlb_fs_parameters = {
};

#ifdef CONFIG_NUMA
+static inline struct shared_policy *hugetlb_get_shared_policy(
+ struct inode *inode)
+{
+ return &HUGETLBFS_I(inode)->policy;
+}
+
static inline void hugetlb_set_vma_policy(struct vm_area_struct *vma,
- struct inode *inode, pgoff_t index)
+ struct shared_policy *policy, pgoff_t index)
{
- vma->vm_policy = mpol_shared_policy_lookup(&HUGETLBFS_I(inode)->policy,
- index);
+ vma->vm_policy = mpol_shared_policy_lookup(policy, index);
}

static inline void hugetlb_drop_vma_policy(struct vm_area_struct *vma)
@@ -116,8 +122,14 @@ static inline void hugetlb_drop_vma_policy(struct vm_area_struct *vma)
mpol_cond_put(vma->vm_policy);
}
#else
+static inline struct shared_policy *hugetlb_get_shared_policy(
+ struct inode *inode)
+{
+ return NULL;
+}
+
static inline void hugetlb_set_vma_policy(struct vm_area_struct *vma,
- struct inode *inode, pgoff_t index)
+ struct shared_policy *policy, pgoff_t index)
{
}

@@ -576,20 +588,30 @@ static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
return 0;
}

+struct hf_args {
+ struct file *file;
+ struct task_struct *parent_task;
+ struct mm_struct *mm;
+ struct shared_policy *shared_policy;
+ struct hstate *hstate;
+ struct address_space *mapping;
+ int error;
+};
+
+static int hugetlbfs_fallocate_chunk(pgoff_t start, pgoff_t end,
+ struct hf_args *args);
+
static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
loff_t len)
{
struct inode *inode = file_inode(file);
struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
- struct address_space *mapping = inode->i_mapping;
struct hstate *h = hstate_inode(inode);
- struct vm_area_struct pseudo_vma;
- struct mm_struct *mm = current->mm;
loff_t hpage_size = huge_page_size(h);
unsigned long hpage_shift = huge_page_shift(h);
- pgoff_t start, index, end;
+ pgoff_t start, end;
+ struct hf_args hf_args;
int error;
- u32 hash;

if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
return -EOPNOTSUPP;
@@ -617,16 +639,66 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
goto out;
}

+ hf_args.file = file;
+ hf_args.parent_task = current;
+ hf_args.mm = current->mm;
+ hf_args.shared_policy = hugetlb_get_shared_policy(inode);
+ hf_args.hstate = h;
+ hf_args.mapping = inode->i_mapping;
+ hf_args.error = 0;
+
+ if (unlikely(hstate_is_gigantic(h))) {
+ /*
+ * Use multiple threads in clear_gigantic_page instead of here,
+ * so just do a 1-threaded hugetlbfs_fallocate_chunk.
+ */
+ error = hugetlbfs_fallocate_chunk(start, end, &hf_args);
+ } else {
+ DEFINE_KTASK_CTL(ctl, hugetlbfs_fallocate_chunk,
+ &hf_args, KTASK_PMD_MINCHUNK);
+
+ error = ktask_run((void *)start, end - start, &ctl);
+ }
+
+ if (error != KTASK_RETURN_SUCCESS && hf_args.error != -EINTR)
+ goto out;
+
+ if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
+ i_size_write(inode, offset + len);
+ inode->i_ctime = current_time(inode);
+out:
+ inode_unlock(inode);
+ return error;
+}
+
+static int hugetlbfs_fallocate_chunk(pgoff_t start, pgoff_t end,
+ struct hf_args *args)
+{
+ struct file *file = args->file;
+ struct task_struct *parent_task = args->parent_task;
+ struct mm_struct *mm = args->mm;
+ struct shared_policy *shared_policy = args->shared_policy;
+ struct hstate *h = args->hstate;
+ struct address_space *mapping = args->mapping;
+ int error = 0;
+ pgoff_t index;
+ struct vm_area_struct pseudo_vma;
+ loff_t hpage_size;
+ u32 hash;
+
+ hpage_size = huge_page_size(h);
+
/*
* Initialize a pseudo vma as this is required by the huge page
* allocation routines. If NUMA is configured, use page index
- * as input to create an allocation policy.
+ * as input to create an allocation policy. Each thread gets its
+ * own pseudo vma because mempolicies can differ by page.
*/
vma_init(&pseudo_vma, mm);
pseudo_vma.vm_flags = (VM_HUGETLB | VM_MAYSHARE | VM_SHARED);
pseudo_vma.vm_file = file;

- for (index = start; index < end; index++) {
+ for (index = start; index < end; ++index) {
/*
* This is supposed to be the vaddr where the page is being
* faulted in, but we have no vaddr here.
@@ -641,13 +713,13 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
* fallocate(2) manpage permits EINTR; we may have been
* interrupted because we are using up too much memory.
*/
- if (signal_pending(current)) {
+ if (signal_pending(parent_task) || signal_pending(current)) {
error = -EINTR;
- break;
+ goto err;
}

/* Set numa allocation policy based on index */
- hugetlb_set_vma_policy(&pseudo_vma, inode, index);
+ hugetlb_set_vma_policy(&pseudo_vma, shared_policy, index);

/* addr is the offset within the file (zero based) */
addr = index * hpage_size;
@@ -672,7 +744,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
if (IS_ERR(page)) {
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
error = PTR_ERR(page);
- goto out;
+ goto err;
}
clear_huge_page(page, addr, pages_per_huge_page(h));
__SetPageUptodate(page);
@@ -680,7 +752,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
if (unlikely(error)) {
put_page(page);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
- goto out;
+ goto err;
}

mutex_unlock(&hugetlb_fault_mutex_table[hash]);
@@ -693,11 +765,11 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
put_page(page);
}

- if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
- i_size_write(inode, offset + len);
- inode->i_ctime = current_time(inode);
-out:
- inode_unlock(inode);
+ return KTASK_RETURN_SUCCESS;
+
+err:
+ args->error = error;
+
return error;
}

--
2.19.1