The patch titled
Subject: mm: shmem: update iocb->ki_pos directly to simplify tmpfs read logic
has been added to the -mm mm-unstable branch. Its filename is
mm-shmem-update-iocb-ki_pos-directly-to-simplify-tmpfs-read-logic.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-update-iocb-ki_pos-directly-to-simplify-tmpfs-read-logic.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm: shmem: update iocb->ki_pos directly to simplify tmpfs read logic
Date: Fri, 18 Oct 2024 11:00:27 +0800
Patch series "Improve the tmpfs large folio read performance", v2.
tmpfs already supports PMD-sized large folios, but the tmpfs read
operation still performs copying at PAGE_SIZE granularity, which is not
perfect. This patchset changes tmpfs to copy data at the folio
granularity, which can improve the read performance.
Use 'fio bs=64k' to read a 1G tmpfs file populated with 2M THPs, and I can
see about 20% performance improvement, and no regression with bs=4k. I
also did some functional testing with the xfstests suite, and I did not
find any regressions with the following xfstests config:
FSTYP=tmpfs
export TEST_DIR=/mnt/tempfs_mnt
export TEST_DEV=/mnt/tempfs_mnt
export SCRATCH_MNT=/mnt/scratchdir
export SCRATCH_DEV=/mnt/scratchdir
This patch (of 2):
Using iocb->ki_pos to check if the read bytes exceeds the file size and to
calculate the bytes to be read can help simplify the code logic.
Meanwhile, this is also a preparation for improving tmpfs large folios
read performance in the following patch.
Link: https://lkml.kernel.org/r/cover.1729218573.git.baolin.wang@xxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/e8863e289577e0dc1e365b5419bf2d1c9a24ae3d.1729218573.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 35 +++++++++++------------------------
1 file changed, 11 insertions(+), 24 deletions(-)
--- a/mm/shmem.c~mm-shmem-update-iocb-ki_pos-directly-to-simplify-tmpfs-read-logic
+++ a/mm/shmem.c
@@ -3096,27 +3096,19 @@ static ssize_t shmem_file_read_iter(stru
unsigned long offset;
int error = 0;
ssize_t retval = 0;
- loff_t *ppos = &iocb->ki_pos;
- index = *ppos >> PAGE_SHIFT;
- offset = *ppos & ~PAGE_MASK;
+ offset = iocb->ki_pos & ~PAGE_MASK;
for (;;) {
struct folio *folio = NULL;
struct page *page = NULL;
- pgoff_t end_index;
unsigned long nr, ret;
- loff_t i_size = i_size_read(inode);
+ loff_t end_offset, i_size = i_size_read(inode);
- end_index = i_size >> PAGE_SHIFT;
- if (index > end_index)
+ if (unlikely(iocb->ki_pos >= i_size))
break;
- if (index == end_index) {
- nr = i_size & ~PAGE_MASK;
- if (nr <= offset)
- break;
- }
+ index = iocb->ki_pos >> PAGE_SHIFT;
error = shmem_get_folio(inode, index, 0, &folio, SGP_READ);
if (error) {
if (error == -EINVAL)
@@ -3138,18 +3130,14 @@ static ssize_t shmem_file_read_iter(stru
* We must evaluate after, since reads (unlike writes)
* are called without i_rwsem protection against truncate
*/
- nr = PAGE_SIZE;
i_size = i_size_read(inode);
- end_index = i_size >> PAGE_SHIFT;
- if (index == end_index) {
- nr = i_size & ~PAGE_MASK;
- if (nr <= offset) {
- if (folio)
- folio_put(folio);
- break;
- }
+ if (unlikely(iocb->ki_pos >= i_size)) {
+ if (folio)
+ folio_put(folio);
+ break;
}
- nr -= offset;
+ end_offset = min_t(loff_t, i_size, iocb->ki_pos + to->count);
+ nr = min_t(loff_t, end_offset - iocb->ki_pos, PAGE_SIZE - offset);
if (folio) {
/*
@@ -3189,8 +3177,8 @@ static ssize_t shmem_file_read_iter(stru
retval += ret;
offset += ret;
- index += offset >> PAGE_SHIFT;
offset &= ~PAGE_MASK;
+ iocb->ki_pos += ret;
if (!iov_iter_count(to))
break;
@@ -3201,7 +3189,6 @@ static ssize_t shmem_file_read_iter(stru
cond_resched();
}
- *ppos = ((loff_t) index << PAGE_SHIFT) + offset;
file_accessed(file);
return retval ? retval : error;
}
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-shmem-fix-khugepaged-activation-policy-for-shmem.patch
mm-shmem-update-iocb-ki_pos-directly-to-simplify-tmpfs-read-logic.patch
mm-shmem-improve-the-tmpfs-large-folio-read-performance.patch
