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Message-ID: <20100106034934.GK3059@balbir.in.ibm.com> Date: Wed, 6 Jan 2010 09:19:34 +0530 From: Balbir Singh <balbir@...ux.vnet.ibm.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH -mm] Shared Page accounting for memory cgroup (v2) * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-01-06 12:18:36]: > On Wed, 6 Jan 2010 08:37:52 +0530 > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-01-06 09:07:08]: > > > > > On Wed, 6 Jan 2010 00:22:26 +0530 > > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > > > > > > > Hi, All, > > > > > > > > No major changes from v1, except for the use of get_mm_rss(). > > > > Kamezawa-San felt that this can be done in user space and I responded > > > > to him with my concerns of doing it in user space. The thread > > > > can be found at http://thread.gmane.org/gmane.linux.kernel.mm/42367. > > > > > > > > If there are no major objections, can I ask for a merge into -mm. > > > > Andrew, the patches are against mmotm 10 December 2009, if there > > > > are some merge conflicts, please let me know, I can rebase after > > > > you release the next mmotm. > > > > > > > > > > The problem is that this isn't "shared" uasge but "considered to be shared" > > > usage. Okay ? > > > > > > > Could you give me your definition of "shared". From the mem cgroup > > perspective, total_rss (which is accumulated) subtracted from the > > count of pages in the LRU which are RSS and FILE_MAPPED is shared, no? > > You consider only "mapped" pages are shared page. That's wrong. > And let's think about your "total_rss - RSS+MAPPED" > > In this typical case, > fork() ---- process(A) > -> fork() --- process(B) > -> process(C) > > total_rss = rss(A) + rss(B) + rss(C) = 3 * rss(A) > Then, > > total_rss - RSS_MAPPED = 2 * rss(A). > > How we call this number ? Is this "shared usage" ? I think no. Why not? The pages in LRU is rss(A) and the total usage is 3*rss(A), shared does not imply shared outside the cgroup. Why do you say it is not shared? > If you want to do this, scan LRU and count the number of really shared pages. A page walk for large number of cases is expensive for a large memory cgroup. > It's much better than detecting "shared pages" via process and will have no > big issue if implemented in proper way. > A walk is not cheap, specifically since the list is protected by zone lru lock and there are now 5 lists. > > I understand that some of the pages that might be shared, show up > > in our LRU and accounting. These are not treated as shared by > > our cgroup, but by other cgroups. > > > > > Then I don't want to provide this misleading value as "official report" from > > > the kernel. And this can be done in userland. > > > > > > > I explained some of the issues of doing this from user space, would > > you be OK if I called them "non-private" pages? > > > > I think I explained there is no issue to do this in user-land. > You did not respond back to the last message of (I thought I convinced you) http://thread.gmane.org/gmane.linux.kernel.mm/42367 -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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