From: Baolin Wang Date: Fri, 18 Oct 2024 03:00:27 +0000 (+0800) Subject: mm: shmem: update iocb->ki_pos directly to simplify tmpfs read logic X-Git-Tag: v6.13-rc1~99^2~115 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f3650ef89b879d63c63f04e98481f7ed4df1119a;p=thirdparty%2Flinux.git 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 Reviewed-by: Yang Shi Cc: David Hildenbrand Cc: Hugh Dickins Cc: Kefeng Wang Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- diff --git a/mm/shmem.c b/mm/shmem.c index ebf39aa0b9ab5..26aaddc52fd1d 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -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; }