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Message-ID: <YbJ3O1qf+9p/HWka@casper.infradead.org>
Date: Thu, 9 Dec 2021 21:38:03 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "Darrick J . Wong " <djwong@...nel.org>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v2 19/28] iomap: Convert __iomap_zero_iter to use a folio
On Mon, Nov 08, 2021 at 04:05:42AM +0000, Matthew Wilcox (Oracle) wrote:
> +++ b/fs/iomap/buffered-io.c
> @@ -881,17 +881,20 @@ EXPORT_SYMBOL_GPL(iomap_file_unshare);
>
> static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
> {
> + struct folio *folio;
> struct page *page;
> int status;
> - unsigned offset = offset_in_page(pos);
> - unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
> + size_t offset, bytes;
>
> - status = iomap_write_begin(iter, pos, bytes, &page);
> + status = iomap_write_begin(iter, pos, length, &page);
This turned out to be buggy. Darrick and I figured out why his tests
were failing and mine weren't; this only shows up with a 4kB block
size filesystem and I was only testing with 1kB block size filesystems.
(at least on x86; I haven't figured out why it passes with 1kB block size
filesystems, so I'm not sure what would be true on other filesystems).
iomap_write_begin() is not prepared to deal with a length that spans a
page boundary. So I'm replacing this patch with the following patches
(whitespace damaged; pick them up from
https://git.infradead.org/users/willy/linux.git/tag/refs/tags/iomap-folio-5.17c
if you want to compile them):
commit 412212960b72
Author: Matthew Wilcox (Oracle) <willy@...radead.org>
Date: Thu Dec 9 15:47:44 2021 -0500
iomap: Allow iomap_write_begin() to be called with the full length
In the future, we want write_begin to know the entire length of the
write so that it can choose to allocate large folios. Pass the full
length in from __iomap_zero_iter() and limit it where necessary.
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index d67108489148..9270db17c435 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -968,6 +968,9 @@ static int gfs2_iomap_page_prepare(struct inode *inode, loff_t pos,
struct gfs2_sbd *sdp = GFS2_SB(inode);
unsigned int blocks;
+ /* gfs2 does not support large folios yet */
+ if (len > PAGE_SIZE)
+ len = PAGE_SIZE;
blocks = ((pos & blockmask) + len + blockmask) >> inode->i_blkbits;
return gfs2_trans_begin(sdp, RES_DINODE + blocks, 0);
}
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 8d7a67655b60..67fcd3b9928d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -632,6 +632,8 @@ static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
goto out_no_page;
}
folio = page_folio(page);
+ if (pos + len > folio_pos(folio) + folio_size(folio))
+ len = folio_pos(folio) + folio_size(folio) - pos;
if (srcmap->type == IOMAP_INLINE)
status = iomap_write_begin_inline(iter, page);
@@ -891,16 +893,19 @@ static s64 __iomap_zero_iter(struct iomap_iter *iter, loff
_t pos, u64 length)
struct page *page;
int status;
unsigned offset = offset_in_page(pos);
- unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
- status = iomap_write_begin(iter, pos, bytes, &page);
+ if (length > UINT_MAX)
+ length = UINT_MAX;
+ status = iomap_write_begin(iter, pos, length, &page);
if (status)
return status;
+ if (length > PAGE_SIZE - offset)
+ length = PAGE_SIZE - offset;
- zero_user(page, offset, bytes);
+ zero_user(page, offset, length);
mark_page_accessed(page);
- return iomap_write_end(iter, pos, bytes, bytes, page);
+ return iomap_write_end(iter, pos, length, length, page);
}
static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
commit 78c747a1b3a1
Author: Matthew Wilcox (Oracle) <willy@...radead.org>
Date: Fri Nov 5 14:24:09 2021 -0400
iomap: Convert __iomap_zero_iter to use a folio
The zero iterator can work in folio-sized chunks instead of page-sized
chunks. This will save a lot of page cache lookups if the file is cached
in large folios.
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Darrick J. Wong <djwong@...nel.org>
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 67fcd3b9928d..bbde6d4f27cd 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -890,20 +890,23 @@ EXPORT_SYMBOL_GPL(iomap_file_unshare);
static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
{
+ struct folio *folio;
struct page *page;
int status;
- unsigned offset = offset_in_page(pos);
+ size_t offset;
if (length > UINT_MAX)
length = UINT_MAX;
status = iomap_write_begin(iter, pos, length, &page);
if (status)
return status;
- if (length > PAGE_SIZE - offset)
- length = PAGE_SIZE - offset;
+ folio = page_folio(page);
- zero_user(page, offset, length);
- mark_page_accessed(page);
+ offset = offset_in_folio(folio, pos);
+ if (length > folio_size(folio) - offset)
+ length = folio_size(folio) - offset;
+ folio_zero_range(folio, offset, length);
+ folio_mark_accessed(folio);
return iomap_write_end(iter, pos, length, length, page);
}
The xfstests that Darrick identified as failing all passed. Running a
full sweep now; then I'll re-run with a 1kB filesystem to be sure that
still passes. Then I'll send another pull request.
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