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Date: Thu, 16 Apr 2009 11:49:18 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> Cc: Andi Kleen <andi@...stfloor.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org> Subject: Re: [RFC][PATCH] proc: export more page flags in /proc/kpageflags On Thu, Apr 16, 2009 at 10:26:51AM +0800, KOSAKI Motohiro wrote: > tatus: RO > Content-Length: 13245 > Lines: 380 > > Hi > > > > > > On Tue, Apr 14, 2009 at 12:37:10PM +0800, KOSAKI Motohiro wrote: > > > > > > > Export the following page flags in /proc/kpageflags, > > > > > > > just in case they will be useful to someone: > > > > > > > > > > > > > > - PG_swapcache > > > > > > > - PG_swapbacked > > > > > > > - PG_mappedtodisk > > > > > > > - PG_reserved > > > > > > PG_reserved should be exported as PG_KERNEL or somesuch. > > > > PG_KERNEL could be misleading. PG_reserved obviously do not cover all > > (or most) kernel pages. So I'd prefer to export PG_reserved as it is. > > > > It seems that the vast amount of free pages are marked PG_reserved: > > Can I review the document at first? > if no good document for administrator, I can't ack exposing PG_reserved. btw, is this the expected behavior to mark so many free pages as PG_reserved? Last time I looked at it, in 2.6.27, the free pages simply don't have any flags set. //Or maybe it's a false reporting of my tool. Will double check. > > # uname -a > > Linux hp 2.6.30-rc2 #157 SMP Wed Apr 15 19:37:49 CST 2009 x86_64 GNU/Linux > > # echo 1 > /proc/sys/vm/drop_caches > > # ./page-types > > flags page-count MB symbolic-flags long-symbolic-flags > > 0x004000 497474 1943 ______________r_____ reserved > > 0x008000 4454 17 _______________o____ compound > > 0x008014 5 0 __R_D__________o____ referenced,dirty,compound > > 0x000020 1 0 _____l______________ lru > > 0x000028 310 1 ___U_l______________ uptodate,lru > > 0x00002c 18 0 __RU_l______________ referenced,uptodate,lru > > 0x000068 80 0 ___U_lA_____________ uptodate,lru,active > > 0x00006c 157 0 __RU_lA_____________ referenced,uptodate,lru,active > > 0x002078 1 0 ___UDlA______b______ uptodate,dirty,lru,active,swapbacked > > 0x00207c 17 0 __RUDlA______b______ referenced,uptodate,dirty,lru,active,swapbacked > > 0x000228 13 0 ___U_l___x__________ uptodate,lru,reclaim > > 0x000400 2085 8 __________B_________ buddy > > "freed" is better? > buddy is implementation technique name. Not compellingly better :-) I'd expect BUDDY to be a well recognized technique, something close to LRU. PG_BUDDY could be documented as: this page is owned by the buddy system, which manages free memory. PG_FREED may seem more newbie friendly, but there will be the classical newbie question: "Why so few freed pages?!" ;-) It's not likely that an administrator not understanding BUDDY will understand many of the other exported page flags. He will have to query the document anyway. And exporting PG_buddy as it is could be the best option for proficient users. > > 0x000804 1 0 __R________m________ referenced,mmap > > 0x002808 10 0 ___U_______m_b______ uptodate,mmap,swapbacked > > 0x000828 1060 4 ___U_l_____m________ uptodate,lru,mmap > > 0x00082c 215 0 __RU_l_____m________ referenced,uptodate,lru,mmap > > 0x000868 189 0 ___U_lA____m________ uptodate,lru,active,mmap > > 0x002868 4187 16 ___U_lA____m_b______ uptodate,lru,active,mmap,swapbacked > > 0x00286c 30 0 __RU_lA____m_b______ referenced,uptodate,lru,active,mmap,swapbacked > > 0x00086c 1012 3 __RU_lA____m________ referenced,uptodate,lru,active,mmap > > 0x002878 3 0 ___UDlA____m_b______ uptodate,dirty,lru,active,mmap,swapbacked > > 0x008880 936 3 _______S___m___o____ slab,mmap,compound > > 0x000880 1602 6 _______S___m________ slab,mmap > > please don't display mmap and coumpound. it expose SLUB implentation detail. > IOW, if slab flag on, please ignore following flags and mapcount. > - PG_active > - PG_error > - PG_private > - PG_compound > > BTW, if the page don't have PG_lru, following member and flags can be used another meanings. > - PG_active > - PG_referenced > - page::_mapcount > - PG_swapbacked > - PG_reclaim > - PG_unevictable > - PG_mlocked > > and, if the page never interact IO layer, following flags can be used another meanings. > - PG_uptodate > - PG_dirty Good point. I also noticed many of these conditional flags. The perceived solution would be to do some filtering if !CONFIG_DEBUG_KERNEL, to not confuse too many administrators. For kernel developers we want to be faithful :-) > > > 0x0088c0 59 0 ______AS___m___o____ active,slab,mmap,compound > > 0x0008c0 49 0 ______AS___m________ active,slab,mmap > > total 513968 2007 > > > And, PageAnon() result seems provide good information if the page stay in lru. Good point! Will add this bit. > > # ./page-areas 0x004000 > > offset len KB > > 0 15 60KB > > 31 4 16KB > > 159 97 388KB > > 4096 2213 8852KB > > 6899 2385 9540KB > > 9497 3 12KB > > 9728 14528 58112KB > > > > > > > > > - PG_private > > > > > > > - PG_private_2 > > > > > > > - PG_owner_priv_1 > > > > > > > > > > > > > > - PG_head > > > > > > > - PG_tail > > > > > > > - PG_compound > > > > > > I would combine these three into a pseudo "large page" flag. > > > > Very neat idea! Patch updated accordingly. > > > > However - one pity I observed: > > > > # ./page-areas 0x008000 > > offset len KB > > 3088 4 16KB > > > > We can no longer tell if the above line means one 4-page hugepage, or two > > 2-page hugepages... Adding PG_COMPOUND_TAIL into the CONFIG_DEBUG_KERNEL block > > can help kernel developers. Or will it be ever cared by administrators? > > > > 341196 2 8KB > > 341202 2 8KB > > 341262 2 8KB > > 341272 8 32KB > > 341296 8 32KB > > 488448 24 96KB > > 488490 2 8KB > > 488496 320 1280KB > > 488842 2 8KB > > 488848 40 160KB > > > > > > > > > > > > > > > > - PG_unevictable > > > > > > > - PG_mlocked > > > > > > > > > > > > > > - PG_poison > > > > > > PG_poison is also useful to export. But since it depends on my > > > patchkit I will pull a patch for that into the HWPOISON series. > > > > That's not a problem - since the PG_poison line is be protected by > > #ifdef CONFIG_MEMORY_FAILURE :-) > > > > > > > > > - PG_unevictable > > > > > > > - PG_mlocked > > > > > > > > this 9 flags shouldn't exported. > > > > I can't imazine administrator use what purpose those flags. > > > > > > I think an abstraced "PG_pinned" or somesuch flag that combines > > > page lock, unevictable, mlocked would be useful for the administrator. > > > > The PG_PINNED abstraction risks hiding useful information. > > The administrator may not only care about the pinned pages, > > but also care _why_ they are pinned, i.e. ramfs.. or mlock? > > > > So it might be good to export them as is, with proper document. > > > > Here is the v2 patch, with flags for kernel hackers numbered from 32. > > Comments are welcome! > > if you can write good document, PG_unevictable is exportable. > but PG_mlock isn't. > > that's implementation tecknique of efficient unevictable pages for mlock. > we can change the future. Yup. That's in line with my vague feeling. For PG_unevictable we can say that the page is owned by the unevictable (non-)lru and not a candidate for LRU page reclaims. But for PG_mlock it's more about an assistant for kernel optimizations and there are no guarantees... Thanks, Fengguang -- 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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