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mm: shmem: update iocb->ki_pos directly to simplify tmpfs read logic 

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@linux.alibaba.com
Link: https://lkml.kernel.org/r/e8863e289577e0dc1e365b5419bf2d1c9a24ae3d.1729218573.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Baolin Wang 2024-10-18 11:00:27 +08:00 committed by Andrew Morton
parent b7f058f827
commit f3650ef89b
1 changed files with 11 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
mm/shmem.c
View File

@ -3093,27 +3093,19 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
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)
@ -3135,18 +3127,14 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
* 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) {
/*
@ -3186,8 +3174,8 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
retval += ret;
offset += ret;
index += offset >> PAGE_SHIFT;
offset &= ~PAGE_MASK;
iocb->ki_pos += ret;
if (!iov_iter_count(to))
break;
@ -3198,7 +3186,6 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
cond_resched();
}
*ppos = ((loff_t) index << PAGE_SHIFT) + offset;
file_accessed(file);
return retval ? retval : error;
}