Messages in this thread | | | Date | Mon, 01 Sep 2008 08:58:32 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][PATCH] Remove cgroup member from struct page |
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KAMEZAWA Hiroyuki wrote: > On Sun, 31 Aug 2008 23:17:56 +0530 > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > >> This is a rewrite of a patch I had written long back to remove struct page >> (I shared the patches with Kamezawa, but never posted them anywhere else). >> I spent the weekend, cleaning them up for 2.6.27-rc5-mmotm (29 Aug 2008). >> > It's just because I think there is no strong requirements for 64bit count/mapcount. > There is no ZERO_PAGE() for ANON (by Nick Piggin. I add him to CC.) > (shmem still use it but impact is not big.) >
I understand the comment, but not it's context. Are you suggesting that the sizeof _count and _mapcount can be reduced? Hence the impact of having a member in struct page is not all that large? I think the patch is definitely very important for 32 bit systems.
>> I've tested the patches on an x86_64 box, I've run a simple test running >> under the memory control group and the same test running concurrently under >> two different groups (and creating pressure within their groups). I've also >> compiled the patch with CGROUP_MEM_RES_CTLR turned off. >> >> Advantages of the patch >> >> 1. It removes the extra pointer in struct page >> >> Disadvantages >> >> 1. It adds an additional lock structure to struct page_cgroup >> 2. Radix tree lookup is not an O(1) operation, once the page is known >> getting to the page_cgroup (pc) is a little more expensive now. >> >> This is an initial RFC for comments >> >> TODOs >> >> 1. Test the page migration changes >> 2. Test the performance impact of the patch/approach >> >> Comments/Reviews? >> > plz wait until lockless page cgroup.... >
That depends, if we can get the lockless page cgroup done quickly, I don't mind waiting, but if it is going to take longer, I would rather push these changes in. There should not be too much overhead in porting lockless page cgroup patch on top of this (remove pc->lock and use pc->flags). I'll help out, so as to avoid wastage of your effort.
> And If you don't support radix-tree-delete(), pre-allocating all at boot is better. >
We do use radix-tree-delete() in the code, please see below. Pre-allocating has the disadvantage that we will pre-allocate even for kernel pages, etc.
> BTW, why pc->lock is necessary ? It increases size of struct page_cgroup and reduce > the advantege of your patch's to half (8bytes -> 4bytes). >
Yes, I've mentioned that as a disadvantage. Are you suggesting that with lockless page cgroup we won't need pc->lock?
> Thanks, > -Kame
-- Balbir
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