From: David Sterba <dsterba@suse.cz>
To: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc: Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>, Nick Terrell <terrelln@fb.com>,
Chris Down <chris@chrisdown.name>, Qu Wenruo <wqu@suse.com>,
Filipe Manana <fdmanana@suse.com>,
Gabriel Niebler <gniebler@suse.com>,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
Ira Weiny <ira.weiny@intel.com>, David Sterba <dsterba@suse.cz>
Subject: Re: [PATCH] btrfs: Replace kmap_atomic() with kmap_local_page()
Date: Thu, 7 Jul 2022 23:32:01 +0200 [thread overview]
Message-ID: <20220707213201.GR15169@twin.jikos.cz> (raw)
In-Reply-To: <20220627174849.29962-1-fmdefrancesco@gmail.com>
On Mon, Jun 27, 2022 at 07:48:49PM +0200, Fabio M. De Francesco wrote:
> kmap_atomic() is being deprecated in favor of kmap_local_page() where it
> is feasible. With kmap_local_page() mappings are per thread, CPU local,
> and not globally visible.
>
> As far as I can see, the kmap_atomic() calls in compression.c and in
> inode.c can be safely converted.
>
> Above all else, David Sterba has confirmed that "The context in
> check_compressed_csum is atomic [...]" and that "kmap_atomic() in inode.c
> [...] also can be replaced by kmap_local_page().".[1]
>
> Therefore, convert all kmap_atomic() calls currently still left in fs/btrfs
> to kmap_local_page().
>
> Tested with xfstests on a QEMU + KVM 32-bits VM with 4GB RAM and booting a
> kernel with HIGHMEM64GB enabled.
>
> [1] https://lore.kernel.org/linux-btrfs/20220601132545.GM20
> 633@twin.jikos.cz/
>
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Suggested-by: David Sterba <dsterba@suse.cz>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Added to the kmap patches, thanks.
> ---
>
> Tests of groups "quick" and "compress" output several errors largely due
> to memory leaks and shift-out-of-bounds. However, these errors are exactly
> the same which are output without this and other conversions of mine to use
> kmap_local_page(). Therefore, it looks like these changes don't introduce
> regressions.
>
> The previous RFC PATCH can be ignored:
> https://lore.kernel.org/lkml/20220624084215.7287-1-fmdefrancesco@gmail.com/
>
> With this patch, in fs/btrfs there are no longer call sites of kmap() and
> kmap_atomic().
>
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -332,9 +332,9 @@ static int insert_inline_extent(struct btrfs_trans_handle *trans,
> cur_size = min_t(unsigned long, compressed_size,
> PAGE_SIZE);
>
> - kaddr = kmap_atomic(cpage);
> + kaddr = kmap_local_page(cpage);
After some cleanups and simplifications in checksumming functions (that
mapped the buffers) only kmap_atomic in insert_inline_extent remains, so
the final patch will be a bit shorter.
> write_extent_buffer(leaf, kaddr, ptr, cur_size);
> - kunmap_atomic(kaddr);
> + kunmap_local(kaddr);
>
> i++;
> ptr += cur_size;
> @@ -345,9 +345,9 @@ static int insert_inline_extent(struct btrfs_trans_handle *trans,
> } else {
> page = find_get_page(inode->vfs_inode.i_mapping, 0);
> btrfs_set_file_extent_compression(leaf, ei, 0);
> - kaddr = kmap_atomic(page);
> + kaddr = kmap_local_page(page);
> write_extent_buffer(leaf, kaddr, ptr, size);
> - kunmap_atomic(kaddr);
> + kunmap_local(kaddr);
> put_page(page);
> }
> btrfs_mark_buffer_dirty(leaf);
prev parent reply other threads:[~2022-07-07 21:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-27 17:48 [PATCH] btrfs: Replace kmap_atomic() with kmap_local_page() Fabio M. De Francesco
2022-06-30 15:46 ` Ira Weiny
2022-07-07 21:32 ` David Sterba [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220707213201.GR15169@twin.jikos.cz \
--to=dsterba@suse.cz \
--cc=chris@chrisdown.name \
--cc=clm@fb.com \
--cc=dsterba@suse.com \
--cc=fdmanana@suse.com \
--cc=fmdefrancesco@gmail.com \
--cc=gniebler@suse.com \
--cc=ira.weiny@intel.com \
--cc=josef@toxicpanda.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=terrelln@fb.com \
--cc=wqu@suse.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).