Commit b2770276 authored by Baolin Wang's avatar Baolin Wang Committed by Euler
Browse files

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

mainline inclusion
from mainline-v6.12-rc1
commit f3650ef89b879d63c63f04e98481f7ed4df1119a
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/IBFSMJ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f3650ef89b879d63c63f04e98481f7ed4df1119a

--------------------------------

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: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: default avatarYang 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarWang Lian <dev01404@linx-info.com>
---
parent 604e996d

mm/shmem.c

+11 −24
Original line number Diff line number Diff line
@@ -3067,27 +3067,19 @@ 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)
@@ -3109,18 +3101,14 @@ 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 (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) {

			/*
@@ -3160,8 +3148,8 @@ 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;
@@ -3172,7 +3160,6 @@ 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;

}