[Devel] Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure)

[KAMEZAWA Hiroyuki]

On Thu, 11 Mar 2010 13:58:47 +0900
Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp> wrote:
> > I'll consider yet another fix for race in account migration if I can.
> > 
> me too.
> 

How about this ? Assume that the race is very rare.

	1. use trylock when updating statistics.
	   If trylock fails, don't account it.

	2. add PCG_FLAG for all status as

+	PCG_ACCT_FILE_MAPPED, /* page is accounted as file rss*/
+	PCG_ACCT_DIRTY, /* page is dirty */
+	PCG_ACCT_WRITEBACK, /* page is being written back to disk */
+	PCG_ACCT_WRITEBACK_TEMP, /* page is used as temporary buffer for FUSE */
+	PCG_ACCT_UNSTABLE_NFS, /* NFS page not yet committed to the server */

	3. At reducing counter, check PCG_xxx flags by
	TESTCLEARPCGFLAG()

This is similar to an _used_ method of LRU accounting. And We can think this
method's error-range never go too bad number. 

I think this kind of fuzzy accounting is enough for writeback status.
Does anyone need strict accounting ?

Thanks,
-Kame

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