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[PATCH 11/12] vfs: increase shrinker batch size

To: linux-fsdevel@xxxxxxxxxxxxxxx
Subject: [PATCH 11/12] vfs: increase shrinker batch size
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 2 Jun 2011 17:01:06 +1000
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <1306998067-27659-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1306998067-27659-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

Now that the per-sb shrinker is responsible for shrinking 2 or more
caches, increase the batch size to keep econmies of scale for
shrinking each cache.  Increase the shrinker batch size to 1024
objects.

To allow for a large increase in batch size, add a conditional
reschedule to prune_icache_sb() so that we don't hold the LRU spin
lock for too long. This mirrors the behaviour of the
__shrink_dcache_sb(), and allows us to increase the batch size
without needing to worry about problems caused by long lock hold
times.

To ensure that filesystems using the per-sb shrinker callouts don't
cause problems, document that the object freeing method must
reschedule appropriately inside loops.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 Documentation/filesystems/vfs.txt |    5 +++++
 fs/super.c                        |    1 +
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/Documentation/filesystems/vfs.txt 
b/Documentation/filesystems/vfs.txt
index dc732d2..2e26973 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -317,6 +317,11 @@ or bottom half).
        the VM is trying to reclaim under GFP_NOFS conditions, hence this
        method does not need to handle that situation itself.
 
+       Implementations must include conditional reschedule calls inside any
+       scanning loop that is done. This allows the VFS to determine
+       appropriate scan batch sizes without having to worry about whether
+       implementations will cause holdoff problems due ot large batch sizes.
+
 Whoever sets up the inode is responsible for filling in the "i_op" field. This
 is a pointer to a "struct inode_operations" which describes the methods that
 can be performed on individual inodes.
diff --git a/fs/super.c b/fs/super.c
index b55f968..323a63e 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -184,6 +184,7 @@ static struct super_block *alloc_super(struct 
file_system_type *type)
 
                s->s_shrink.seeks = DEFAULT_SEEKS;
                s->s_shrink.shrink = prune_super;
+               s->s_shrink.batch = 1024;
        }
 out:
        return s;
-- 
1.7.5.1

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