linux-kernel - Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

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Message-Id: <20100617152312.43e84eb0.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 17 Jun 2010 15:23:12 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

On Thu, 17 Jun 2010 02:16:47 -0400
Christoph Hellwig <hch@...radead.org> wrote:

> On Thu, Jun 17, 2010 at 09:25:38AM +0900, KAMEZAWA Hiroyuki wrote:
> > 
> > BTW, why xbf_buf_create() use GFP_KERNEL even if it can be blocked ?
> > memory cgroup just limits pages for users, then, doesn't intend to
> > limit kernel pages.
> 
> You mean xfs_buf_allocate?  It doesn't in the end.  It goes through the
> xfs_kmem helper which clear __GFP_FS if we're currently inside a
> filesystem transaction (PF_FSTRANS is set) or a caller specificly
> requested it to be disabled even without that by passig the
> XBF_DONT_BLOCK flag.
> 
Ah, sorry. My question was wrong.

If xfs_buf_allocate() is not for pages on LRU but for kernel memory,
memory cgroup has no reason to charge against it because we can't reclaim
memory which is not on LRU.

Then, I wonder I may have to add following check 

	if (!(gfp_mask & __GFP_RECLAIMABLE)) {
		/* ignore this. we just charge against reclaimable memory on LRU. */
		return 0;
	}

to mem_cgroup_charge_cache() which is a hook for accounting page-cache.


Thanks,
-Kame

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