Re: [PATCH] tools/vm/page-types.c: page-cache sniffing feature

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

Hi Konstantin,

This patch is already in upstream, but I have another idea of implementing
the similar feature. So let me review this now, and I'll post patches to
complement this patch.

On Wed, Feb 26, 2014 at 11:57:23AM +0400, Konstantin Khlebnikov wrote:
> After this patch 'page-types' can walk on filesystem mappings and analize
> populated page cache pages mostly without disturbing its state.
> 
> It maps chunk of file, marks VMA as MADV_RANDOM to turn off readahead,
> pokes VMA via mincore() to determine cached pages, triggers page-fault
> only for them, and finally gathers information via pagemap/kpageflags.
> Before unmap it marks VMA as MADV_SEQUENTIAL for ignoring reference bits.

I think that with this patch page-types *does* disturb page cache (not only
of the target file) because it newly populates the pages not faulted in
when page-types starts, which rotates LRU list and adds memory pressure.
To minimize the measurement-disturbance, we need some help in the kernel side.

> 
> usage: page-types -f <path>
> 
> If <path> is directory it will analyse all files in all subdirectories.

I think -f was reserved for "Walk file address space", so doing file tree
walk looks to me overkill. You can add "directory mode (-d) for this purpose,
although it seems to me that we can/should do this (for example) by combining
with find command. I can show you the example in my patch later.

> Symlinks are not followed as well as mount points. Hardlinks aren't handled,
> they'll be dumbed as many times as they are found. Recursive walk brings all
> dentries into dcache and populates page cache of block-devices aka 'Buffers'.
> 
> Probably it's worth to add ioctl for dumping file page cache as array of PFNs
> as a replacement for this hackish juggling with mmap/madvise/mincore/pagemap.
> 
> Also recursive walk could be replaced with dumping cached inodes via some ioctl
> or debugfs interface followed by openning them via open_by_handle_at, this
> would fix hardlinks handling and unneeded population of dcache and buffers.
> This interface might be used as data source for constructing readahead plans
> and for background optimizations of actively used files.
> 
> collateral changes:
> + fix 64-bit LFS: define _FILE_OFFSET_BITS instead of _LARGEFILE64_SOURCE
> + replace lseek + read with single pread

Good, thanks.

> + make show_page_range() reusable after flush
> 
> 
> usage example:
> 
> ~/src/linux/tools/vm$ sudo ./page-types -L -f page-types
> foffset	offset	flags
> page-types	Inode: 2229277	Size: 89065 (22 pages)
> Modify: Tue Feb 25 12:00:59 2014 (162 seconds ago)
> Access: Tue Feb 25 12:01:00 2014 (161 seconds ago)

I don't see why page-types needs to show these information.
We have many other tools to check file info, so this small program should
focus on page related things.

Thanks,
Naoya Horiguchi

> 0	3cbf3b	__RU_lA____M________________________
> 1	38946a	__RU_lA____M________________________
> 2	1a3cec	__RU_lA____M________________________
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> 6	2e436a	__RU_lA_____________________________
> 7	29a35e	___U_lA_____________________________
> 8	2de86e	___U_lA_____________________________
> 9	3bdfb4	___U_lA_____________________________
> 10	3cd8a3	___U_lA_____________________________
> 11	2afa50	___U_lA_____________________________
> 12	2534c2	___U_lA_____________________________
> 13	1b7a40	___U_lA_____________________________
> 14	17b0be	___U_lA_____________________________
> 15	392b0c	___U_lA_____________________________
> 16	3ba46a	__RU_lA_____________________________
> 17	397dc8	___U_lA_____________________________
> 18	1f2a36	___U_lA_____________________________
> 19	21fd30	__RU_lA_____________________________
> 20	2c35ba	__RU_l______________________________
> 21	20f181	__RU_l______________________________
> 
> 
>              flags	page-count       MB  symbolic-flags			long-symbolic-flags
> 0x000000000000002c	         2        0  __RU_l______________________________	referenced,uptodate,lru
> 0x0000000000000068	        11        0  ___U_lA_____________________________	uptodate,lru,active
> 0x000000000000006c	         4        0  __RU_lA_____________________________	referenced,uptodate,lru,active
> 0x000000000000086c	         5        0  __RU_lA____M________________________	referenced,uptodate,lru,active,mmap
>              total	        22        0
> 
> 
> 
> ~/src/linux/tools/vm$ sudo ./page-types -f /
>              flags	page-count       MB  symbolic-flags			long-symbolic-flags
> 0x0000000000000028	     21761       85  ___U_l______________________________	uptodate,lru
> 0x000000000000002c	    127279      497  __RU_l______________________________	referenced,uptodate,lru
> 0x0000000000000068	     74160      289  ___U_lA_____________________________	uptodate,lru,active
> 0x000000000000006c	     84469      329  __RU_lA_____________________________	referenced,uptodate,lru,active
> 0x000000000000007c	         1        0  __RUDlA_____________________________	referenced,uptodate,dirty,lru,active
> 0x0000000000000228	       370        1  ___U_l___I__________________________	uptodate,lru,reclaim
> 0x0000000000000828	        49        0  ___U_l_____M________________________	uptodate,lru,mmap
> 0x000000000000082c	       126        0  __RU_l_____M________________________	referenced,uptodate,lru,mmap
> 0x0000000000000868	       137        0  ___U_lA____M________________________	uptodate,lru,active,mmap
> 0x000000000000086c	     12890       50  __RU_lA____M________________________	referenced,uptodate,lru,active,mmap
>              total	    321242     1254
> 
> Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
> ---
>  tools/vm/page-types.c |  170 ++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 152 insertions(+), 18 deletions(-)

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