From: Dave Chinner <david@fromorbit.com>
To: Nick Piggin <npiggin@kernel.dk>
Cc: linux-fsdevel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@ZenIV.linux.org.uk>, Christoph Hellwig <hch@lst.de>
Subject: Re: [patch] fs: use fast counters for vfs caches
Date: Thu, 9 Dec 2010 16:43:43 +1100 [thread overview]
Message-ID: <20101209054343.GA8259@dastard> (raw)
In-Reply-To: <20101129105733.GA3241@amd>
On Mon, Nov 29, 2010 at 09:57:33PM +1100, Nick Piggin wrote:
> Hey,
>
> What was the reason behind not using my approach to use fast per-cpu
> counters for inode and dentry counters, and instead using the
> percpu_counter lib (which is not useful unless very fast approximate
> access to the global counter is required, or performance is not
> critical, which is somewhat of an oxymoron if you're using per-counters
> in the first place). It is a difference between this:
Hi Nick - sorry for being slow to answer this - I only just found
this email.
The reason for using the generic counters is because the shrinkers
read the current value of the global counter on every call and hence
they can be read thousands of times a second. The only way to do that
efficiently is to use the approximately value the generic counters
provide.
IIRC, it's also used in a couple of places in the writeback code as
well, but that is significantly fewer reads of the summed value.
It's probably best to revisit this once the shrinkers no longer use
a global counter value.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2010-12-09 5:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-29 10:57 [patch] fs: use fast counters for vfs caches Nick Piggin
2010-12-09 5:43 ` Dave Chinner [this message]
2010-12-09 6:16 ` Nick Piggin
2010-12-09 6:40 ` Nick Piggin
2010-12-10 4:51 ` [patch 1/2] fs: revert percpu nr_unused counters for dentry and inodes Nick Piggin
2010-12-10 4:55 ` [patch 2/2] fs: use fast counters for vfs caches Nick Piggin
2010-12-09 7:45 ` [PATCH] fs: use approximate counter values for inodes and dentries. (was Re: [patch] fs: use fast counters for vfs caches) Dave Chinner
2010-12-09 12:24 ` Nick Piggin
2010-12-09 23:30 ` Dave Chinner
2010-12-10 2:23 ` Nick Piggin
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