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Message-ID: <CAHbLzkoEtyKjUCChaAizAAnEXet3519q7Xg4nOm7aE4QdfeFjA@mail.gmail.com>
Date: Fri, 18 Oct 2024 11:38:36 -0700
From: Yang Shi <shy828301@...il.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, willy@...radead.org,
david@...hat.com, wangkefeng.wang@...wei.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm: shmem: improve the tmpfs large folio read performance
On Thu, Oct 17, 2024 at 8:00 PM Baolin Wang
<baolin.wang@...ux.alibaba.com> wrote:
>
> The tmpfs has already supported the PMD-sized large folios, but the tmpfs
> read operation still performs copying at the PAGE SIZE granularity, which
> is unreasonable. This patch changes to copy data at the folio granularity,
> which can improve the read performance, as well as changing to use folio
> related functions.
>
> Moreoever, if a large folio has a subpage that is hwpoisoned, it will still
> fallback to page granularity copying.
s/Moreoever/Moreover
>
> 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.
> Before the patch:
> READ: bw=10.0GiB/s
>
> After the patch:
> READ: bw=12.0GiB/s
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
The patch looks fine to me. Reviewed-by: Yang Shi <shy828301@...il.com>
> ---
> mm/shmem.c | 34 ++++++++++++++++++++++++----------
> 1 file changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 93642aa8d1aa..cbefd9801f6b 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3107,13 +3107,13 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> int error = 0;
> ssize_t retval = 0;
>
> - offset = iocb->ki_pos & ~PAGE_MASK;
> -
> for (;;) {
> struct folio *folio = NULL;
> struct page *page = NULL;
> unsigned long nr, ret;
> loff_t end_offset, i_size = i_size_read(inode);
> + bool fallback_page_copy = false;
> + size_t fsize;
>
> if (unlikely(iocb->ki_pos >= i_size))
> break;
> @@ -3134,6 +3134,10 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> error = -EIO;
> break;
> }
> +
> + if (folio_test_large(folio) &&
> + folio_test_has_hwpoisoned(folio))
> + fallback_page_copy = true;
> }
>
> /*
> @@ -3147,7 +3151,12 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> break;
> }
> 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 && likely(!fallback_page_copy))
> + fsize = folio_size(folio);
> + else
> + fsize = PAGE_SIZE;
> + offset = iocb->ki_pos & (fsize - 1);
> + nr = min_t(loff_t, end_offset - iocb->ki_pos, fsize - offset);
>
> if (folio) {
> /*
> @@ -3155,10 +3164,15 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> * virtual addresses, take care about potential aliasing
> * before reading the page on the kernel side.
> */
> - if (mapping_writably_mapped(mapping))
> - flush_dcache_page(page);
> + if (mapping_writably_mapped(mapping)) {
> + if (likely(!fallback_page_copy))
> + flush_dcache_folio(folio);
> + else
> + flush_dcache_page(page);
> + }
> +
> /*
> - * Mark the page accessed if we read the beginning.
> + * Mark the folio accessed if we read the beginning.
> */
> if (!offset)
> folio_mark_accessed(folio);
> @@ -3166,9 +3180,11 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> * Ok, we have the page, and it's up-to-date, so
> * now we can copy it to user space...
> */
> - ret = copy_page_to_iter(page, offset, nr, to);
> + if (likely(!fallback_page_copy))
> + ret = copy_folio_to_iter(folio, offset, nr, to);
> + else
> + ret = copy_page_to_iter(page, offset, nr, to);
> folio_put(folio);
> -
> } else if (user_backed_iter(to)) {
> /*
> * Copy to user tends to be so well optimized, but
> @@ -3186,8 +3202,6 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> }
>
> retval += ret;
> - offset += ret;
> - offset &= ~PAGE_MASK;
> iocb->ki_pos += ret;
>
> if (!iov_iter_count(to))
> --
> 2.39.3
>
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