[PATCH] btrfs: remove unnecessary attempt do drop extent maps after adding inline extent

[PATCH] btrfs: remove unnecessary attempt do drop extent maps after adding inline extent

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

At inode.c:cow_file_range_inline(), after we insert the inline extent
in the fs/subvolume btree, we call btrfs_drop_extent_cache() to drop
all extent maps in the file range, however that is not necessary because
we have already done it in the call to btrfs_drop_extents(), which calls
btrfs_drop_extent_cache() for us, and since at this point we have the file
range locked in the inode's iotree (we are in the writeback path), we know
no other task can come in and read stale file extent items or find none
and therefore create either stale extent maps or an extent map that
represens a hole.

So just remove that unnecessary call to btrfs_drop_extent_cache(), as it's
doing nothing and only wasting time. This call has been around since 2008,
introduced in commit c8b978188c9a ("Btrfs: Add zlib compression support"),
but even back then it seems it was not necessary, since we had the range
locked in the inode's iotree and the call to btrfs_drop_extents() already
used to always call btrfs_drop_extent_cache().

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/inode.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 84a75cf86d88..0a2ee8983528 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -392,7 +392,6 @@ static noinline int cow_file_range_inline(struct btrfs_inode *inode, u64 start,
 	}
 
 	set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &inode->runtime_flags);
-	btrfs_drop_extent_cache(inode, start, aligned_end - 1, 0);
 out:
 	/*
 	 * Don't forget to free the reserved space, as for inlined extent
-- 
2.28.0

Re: [PATCH] btrfs: remove unnecessary attempt do drop extent maps after adding inline extent

[Josef Bacik]

On 11/13/20 6:24 AM, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> At inode.c:cow_file_range_inline(), after we insert the inline extent
> in the fs/subvolume btree, we call btrfs_drop_extent_cache() to drop
> all extent maps in the file range, however that is not necessary because
> we have already done it in the call to btrfs_drop_extents(), which calls
> btrfs_drop_extent_cache() for us, and since at this point we have the file
> range locked in the inode's iotree (we are in the writeback path), we know
> no other task can come in and read stale file extent items or find none
> and therefore create either stale extent maps or an extent map that
> represens a hole.
> 
> So just remove that unnecessary call to btrfs_drop_extent_cache(), as it's
> doing nothing and only wasting time. This call has been around since 2008,
> introduced in commit c8b978188c9a ("Btrfs: Add zlib compression support"),
> but even back then it seems it was not necessary, since we had the range
> locked in the inode's iotree and the call to btrfs_drop_extents() already
> used to always call btrfs_drop_extent_cache().
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH] btrfs: remove unnecessary attempt do drop extent maps after adding inline extent

[David Sterba]

On Fri, Nov 13, 2020 at 11:24:17AM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> At inode.c:cow_file_range_inline(), after we insert the inline extent
> in the fs/subvolume btree, we call btrfs_drop_extent_cache() to drop
> all extent maps in the file range, however that is not necessary because
> we have already done it in the call to btrfs_drop_extents(), which calls
> btrfs_drop_extent_cache() for us, and since at this point we have the file
> range locked in the inode's iotree (we are in the writeback path), we know
> no other task can come in and read stale file extent items or find none
> and therefore create either stale extent maps or an extent map that
> represens a hole.
> 
> So just remove that unnecessary call to btrfs_drop_extent_cache(), as it's
> doing nothing and only wasting time. This call has been around since 2008,
> introduced in commit c8b978188c9a ("Btrfs: Add zlib compression support"),
> but even back then it seems it was not necessary, since we had the range
> locked in the inode's iotree and the call to btrfs_drop_extents() already
> used to always call btrfs_drop_extent_cache().
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.