From: "Darrick J. Wong" <djwong@kernel.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
Wang Yugui <wangyugui@e16-tech.com>,
Dave Chinner <david@fromorbit.com>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v2 7/7] iomap: Copy larger chunks from userspace
Date: Sun, 4 Jun 2023 11:29:52 -0700 [thread overview]
Message-ID: <20230604182952.GH72241@frogsfrogsfrogs> (raw)
In-Reply-To: <20230602222445.2284892-8-willy@infradead.org>
On Fri, Jun 02, 2023 at 11:24:44PM +0100, Matthew Wilcox (Oracle) wrote:
> If we have a large folio, we can copy in larger chunks than PAGE_SIZE.
> Start at the maximum page cache size and shrink by half every time we
> hit the "we are short on memory" problem.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> fs/iomap/buffered-io.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index a10f9c037515..10434b07e0f9 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -768,6 +768,7 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
> static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> {
> loff_t length = iomap_length(iter);
> + size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
> loff_t pos = iter->pos;
> ssize_t written = 0;
> long status = 0;
> @@ -776,15 +777,13 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>
> do {
> struct folio *folio;
> - struct page *page;
> - unsigned long offset; /* Offset into pagecache page */
> - unsigned long bytes; /* Bytes to write to page */
> + size_t offset; /* Offset into folio */
> + unsigned long bytes; /* Bytes to write to folio */
> size_t copied; /* Bytes copied from user */
>
> - offset = offset_in_page(pos);
> - bytes = min_t(unsigned long, PAGE_SIZE - offset,
> - iov_iter_count(i));
> again:
> + offset = pos & (chunk - 1);
> + bytes = min(chunk - offset, iov_iter_count(i));
> status = balance_dirty_pages_ratelimited_flags(mapping,
> bdp_flags);
> if (unlikely(status))
> @@ -814,11 +813,14 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> if (iter->iomap.flags & IOMAP_F_STALE)
> break;
>
> - page = folio_file_page(folio, pos >> PAGE_SHIFT);
> + offset = offset_in_folio(folio, pos);
> + if (bytes > folio_size(folio) - offset)
> + bytes = folio_size(folio) - offset;
> +
> if (mapping_writably_mapped(mapping))
> - flush_dcache_page(page);
> + flush_dcache_folio(folio);
>
> - copied = copy_page_from_iter_atomic(page, offset, bytes, i);
> + copied = copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
I think I've gotten lost in the weeds. Does copy_page_from_iter_atomic
actually know how to deal with a multipage folio? AFAICT it takes a
page, kmaps it, and copies @bytes starting at @offset in the page. If
a caller feeds it a multipage folio, does that all work correctly? Or
will the pagecache split multipage folios as needed to make it work
right?
If we create a 64k folio at pos 0 and then want to write a byte at pos
40k, does __filemap_get_folio break up the 64k folio so that the folio
returned by iomap_get_folio starts at 40k? Or can the iter code handle
jumping ten pages into a 16-page folio and I just can't see it?
(Allergies suddenly went from 0 to 9, engage breaindead mode...)
--D
>
> status = iomap_write_end(iter, pos, bytes, copied, folio);
>
> @@ -835,6 +837,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> */
> if (copied)
> bytes = copied;
> + if (chunk > PAGE_SIZE)
> + chunk /= 2;
> goto again;
> }
> pos += status;
> --
> 2.39.2
>
next prev parent reply other threads:[~2023-06-04 18:29 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-02 22:24 [PATCH v2 0/7] Create large folios in iomap buffered write path Matthew Wilcox (Oracle)
2023-06-02 22:24 ` [PATCH v2 1/7] iomap: Remove large folio handling in iomap_invalidate_folio() Matthew Wilcox (Oracle)
2023-06-04 17:58 ` Darrick J. Wong
2023-06-05 7:11 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 2/7] doc: Correct the description of ->release_folio Matthew Wilcox (Oracle)
2023-06-04 17:55 ` Darrick J. Wong
2023-06-04 20:10 ` Matthew Wilcox
2023-06-04 20:33 ` Darrick J. Wong
2023-06-05 13:11 ` Matthew Wilcox
2023-06-05 15:07 ` Darrick J. Wong
2023-06-05 7:12 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 3/7] iomap: Remove unnecessary test from iomap_release_folio() Matthew Wilcox (Oracle)
2023-06-04 18:01 ` Darrick J. Wong
2023-06-04 21:39 ` Matthew Wilcox
2023-06-05 21:10 ` Ritesh Harjani
2023-06-05 7:13 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 4/7] filemap: Add fgp_t typedef Matthew Wilcox (Oracle)
2023-06-04 18:02 ` Darrick J. Wong
2023-06-05 7:14 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 5/7] filemap: Allow __filemap_get_folio to allocate large folios Matthew Wilcox (Oracle)
2023-06-04 18:09 ` Darrick J. Wong
2023-06-04 21:48 ` Matthew Wilcox
2023-06-05 15:21 ` Darrick J. Wong
2023-06-05 7:16 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 6/7] iomap: Create large folios in the buffered write path Matthew Wilcox (Oracle)
2023-06-04 18:10 ` Darrick J. Wong
2023-06-05 7:16 ` Christoph Hellwig
2023-06-02 22:24 ` [PATCH v2 7/7] iomap: Copy larger chunks from userspace Matthew Wilcox (Oracle)
2023-06-04 18:29 ` Darrick J. Wong [this message]
2023-06-04 22:11 ` Matthew Wilcox
2023-06-05 8:25 ` Yin, Fengwei
2023-06-06 18:07 ` Matthew Wilcox
2023-06-07 2:21 ` Yin Fengwei
2023-06-07 5:33 ` Yin, Fengwei
2023-06-07 15:55 ` Matthew Wilcox
2023-06-08 1:22 ` Yin Fengwei
2023-06-07 6:40 ` Yin Fengwei
2023-06-07 15:56 ` Matthew Wilcox
2023-06-04 0:19 ` [PATCH v2 0/7] Create large folios in iomap buffered write path Wang Yugui
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