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Date: Thu, 16 Apr 2009 11:26:51 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Wu Fengguang <fengguang.wu@...el.com>
Cc: kosaki.motohiro@...fujitsu.com, 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
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.
> # 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.
> 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
> 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.
> # ./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.
> Thanks,
> Fengguang
> ---
>
> Export all available page flags in /proc/kpageflags, plus two pseudo ones.
> This increases the total number of exported page flags to 26.
>
> TODO: more document
>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: Alexey Dobriyan <adobriyan@...il.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
> fs/proc/page.c | 122 +++++++++++++++++++++++++++++++++++------------
> 1 file changed, 91 insertions(+), 31 deletions(-)
>
> --- mm.orig/fs/proc/page.c
> +++ mm/fs/proc/page.c
> @@ -68,20 +68,96 @@ static const struct file_operations proc
>
> /* These macros are used to decouple internal flags from exported ones */
>
> -#define KPF_LOCKED 0
> -#define KPF_ERROR 1
> -#define KPF_REFERENCED 2
> -#define KPF_UPTODATE 3
> -#define KPF_DIRTY 4
> -#define KPF_LRU 5
> -#define KPF_ACTIVE 6
> -#define KPF_SLAB 7
> -#define KPF_WRITEBACK 8
> -#define KPF_RECLAIM 9
> -#define KPF_BUDDY 10
> +#define KPF_LOCKED 0
> +#define KPF_ERROR 1
> +#define KPF_REFERENCED 2
> +#define KPF_UPTODATE 3
> +#define KPF_DIRTY 4
> +#define KPF_LRU 5
> +#define KPF_ACTIVE 6
> +#define KPF_SLAB 7
> +#define KPF_WRITEBACK 8
> +#define KPF_RECLAIM 9
> +#define KPF_BUDDY 10
> +
> +/* new additions in 2.6.31 */
> +#define KPF_MMAP 11
> +#define KPF_SWAPCACHE 12
> +#define KPF_SWAPBACKED 13
> +#define KPF_RESERVED 14
> +#define KPF_COMPOUND 15
> +#define KPF_UNEVICTABLE 16
> +#define KPF_MLOCKED 17
> +#define KPF_POISON 18
> +#define KPF_NOPAGE 19
> +
> +/* kernel hacking assistances */
> +#define KPF_MAPPEDTODISK 32
> +#define KPF_PRIVATE 33
> +#define KPF_PRIVATE2 34
> +#define KPF_OWNER_PRIVATE 35
> +#define KPF_ARCH 36
> +#define KPF_UNCACHED 37
>
> #define kpf_copy_bit(flags, dstpos, srcpos) (((flags >> srcpos) & 1) << dstpos)
>
> +u64 get_uflags(struct page *page)
> +{
> + u64 kflags;
> + u64 uflags;
> +
> + if (!page)
> + return 1 << KPF_NOPAGE;
> +
> + kflags = page->flags;
> + uflags = 0;
> +
> + if (page_mapped(page))
> + uflags |= 1 << KPF_MMAP;
> +
> + uflags |= kpf_copy_bit(kflags, KPF_LOCKED, PG_locked);
> + uflags |= kpf_copy_bit(kflags, KPF_ERROR, PG_error);
> + uflags |= kpf_copy_bit(kflags, KPF_REFERENCED, PG_referenced);
> + uflags |= kpf_copy_bit(kflags, KPF_UPTODATE, PG_uptodate);
> + uflags |= kpf_copy_bit(kflags, KPF_DIRTY, PG_dirty);
> + uflags |= kpf_copy_bit(kflags, KPF_LRU, PG_lru) ;
> + uflags |= kpf_copy_bit(kflags, KPF_ACTIVE, PG_active);
> + uflags |= kpf_copy_bit(kflags, KPF_SLAB, PG_slab);
> + uflags |= kpf_copy_bit(kflags, KPF_WRITEBACK, PG_writeback);
> + uflags |= kpf_copy_bit(kflags, KPF_RECLAIM, PG_reclaim);
> + uflags |= kpf_copy_bit(kflags, KPF_BUDDY, PG_buddy);
> +
> + uflags |= kpf_copy_bit(kflags, KPF_SWAPCACHE, PG_swapcache);
> + uflags |= kpf_copy_bit(kflags, KPF_SWAPBACKED, PG_swapbacked);
> + uflags |= kpf_copy_bit(kflags, KPF_RESERVED, PG_reserved);
> +#ifdef CONFIG_PAGEFLAGS_EXTENDED
> + uflags |= kpf_copy_bit(kflags, KPF_COMPOUND, PG_head);
> + uflags |= kpf_copy_bit(kflags, KPF_COMPOUND, PG_tail);
> +#else
> + uflags |= kpf_copy_bit(kflags, KPF_COMPOUND, PG_compound);
> +#endif
> +#ifdef CONFIG_UNEVICTABLE_LRU
> + uflags |= kpf_copy_bit(kflags, KPF_UNEVICTABLE, PG_unevictable);
> + uflags |= kpf_copy_bit(kflags, KPF_MLOCKED, PG_mlocked);
> +#endif
> +#ifdef CONFIG_MEMORY_FAILURE
> + uflags |= kpf_copy_bit(kflags, KPF_POISON, PG_poison);
> +#endif
> +
> +#ifdef CONFIG_DEBUG_KERNEL
> + uflags |= kpf_copy_bit(kflags, KPF_MAPPEDTODISK, PG_mappedtodisk);
> + uflags |= kpf_copy_bit(kflags, KPF_PRIVATE, PG_private);
> + uflags |= kpf_copy_bit(kflags, KPF_PRIVATE2, PG_private_2);
> + uflags |= kpf_copy_bit(kflags, KPF_OWNER_PRIVATE, PG_owner_priv_1);
> + uflags |= kpf_copy_bit(kflags, KPF_ARCH, PG_arch_1);
> +#ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
> + uflags |= kpf_copy_bit(kflags, KPF_UNCACHED, PG_uncached);
> +#endif
> +#endif
> +
> + return uflags;
> +};
> +
> static ssize_t kpageflags_read(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> {
> @@ -90,7 +166,6 @@ static ssize_t kpageflags_read(struct fi
> unsigned long src = *ppos;
> unsigned long pfn;
> ssize_t ret = 0;
> - u64 kflags, uflags;
>
> pfn = src / KPMSIZE;
> count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
> @@ -98,32 +173,17 @@ static ssize_t kpageflags_read(struct fi
> return -EINVAL;
>
> while (count > 0) {
> - ppage = NULL;
> if (pfn_valid(pfn))
> ppage = pfn_to_page(pfn);
> - pfn++;
> - if (!ppage)
> - kflags = 0;
> else
> - kflags = ppage->flags;
> -
> - uflags = kpf_copy_bit(kflags, KPF_LOCKED, PG_locked) |
> - kpf_copy_bit(kflags, KPF_ERROR, PG_error) |
> - kpf_copy_bit(kflags, KPF_REFERENCED, PG_referenced) |
> - kpf_copy_bit(kflags, KPF_UPTODATE, PG_uptodate) |
> - kpf_copy_bit(kflags, KPF_DIRTY, PG_dirty) |
> - kpf_copy_bit(kflags, KPF_LRU, PG_lru) |
> - kpf_copy_bit(kflags, KPF_ACTIVE, PG_active) |
> - kpf_copy_bit(kflags, KPF_SLAB, PG_slab) |
> - kpf_copy_bit(kflags, KPF_WRITEBACK, PG_writeback) |
> - kpf_copy_bit(kflags, KPF_RECLAIM, PG_reclaim) |
> - kpf_copy_bit(kflags, KPF_BUDDY, PG_buddy);
> + ppage = NULL;
>
> - if (put_user(uflags, out++)) {
> + if (put_user(get_uflags(ppage), out)) {
> ret = -EFAULT;
> break;
> }
> -
> + out++;
> + pfn++;
> count -= KPMSIZE;
> }
>
>
> --
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