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Re: [PATCH 10/10] xfs: don't cache inodes read through bulkstat

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 10/10] xfs: don't cache inodes read through bulkstat
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 15 Mar 2012 13:14:26 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1331095828-28742-11-git-send-email-david@xxxxxxxxxxxxx>
References: <1331095828-28742-1-git-send-email-david@xxxxxxxxxxxxx> <1331095828-28742-11-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Wed, Mar 07, 2012 at 03:50:28PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> When we read inodes via bulkstat, we generally only read them once
> and then throw them away - they never get used again. If we retain
> them in cache, then it simply causes the working set of inodes and
> other cached items to be reclaimed just so the inode cache can grow.
> 
> Avoid this problem by marking inodes read by bulkstat as not to be
> cached and check this flag in .drop_inode to determine whether the
> inode should be added to the VFS LRU or not. If the inode lookup
> hits an already cached inode, then don't set the flag. If the inode
> lookup hits an inode marked with no cache flag, remove the flag and
> allow it to be cached once the current reference goes away.
> 
> Inodes marked as not cached will get cleaned up by the background
> inode reclaim or via memory pressure, so they will still generate
> some short term cache pressure. They will, however, be reclaimed
> much sooner and in preference to cache hot inodes.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_iget.c   |    8 ++++++--
>  fs/xfs/xfs_inode.h  |    4 +++-
>  fs/xfs/xfs_itable.c |    3 ++-
>  fs/xfs/xfs_super.c  |   17 +++++++++++++++++
>  4 files changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
> index 93fc1dc..20ddb1e 100644
> --- a/fs/xfs/xfs_iget.c
> +++ b/fs/xfs/xfs_iget.c
> @@ -290,7 +290,7 @@ xfs_iget_cache_hit(
>       if (lock_flags != 0)
>               xfs_ilock(ip, lock_flags);
>  
> -     xfs_iflags_clear(ip, XFS_ISTALE);
> +     xfs_iflags_clear(ip, XFS_ISTALE | XFS_IDONTCACHE);

If XFS_IGET_DONTCACHE is set, maybe you don't want to clear
XFS_IDONTCACHE.

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