* Keiichi KII <k-keiichi@xxxxxxxxxxxxx> [2010-02-04 21:17:35]:
> Hello,
>
> This is v3 of a patchset to add some tracepoints for pagecache.
>
> I would propose several tracepoints for tracing pagecache behavior and
> a script for these.
> By using both the tracepoints and the script, we can analysis pagecache behavior
> like usage or hit ratio with high resolution like per process or per file.
> Example output of the script looks like:
>
> [process list]
> o yum-3215
> cache find cache hit cache hit
> device inode count count ratio
> --------------------------------------------------------
> 253:0 16 34434 34130 99.12%
> 253:0 198 9692 9463 97.64%
> 253:0 639 647 628 97.06%
> 253:0 778 32 29 90.62%
> 253:0 7305 50225 49005 97.57%
> 253:0 144217 12 10 83.33%
> 253:0 262775 16 13 81.25%
> *snip*
Very nice, we should be able to sum these to get a system wide view
>
> -------------------------------------------------------------------------------
>
> [file list]
> device cached
> (maj:min) inode pages
> --------------------------------
> 253:0 16 5752
> 253:0 198 2233
> 253:0 639 51
> 253:0 778 86
> 253:0 7305 12307
> 253:0 144217 11
> 253:0 262775 39
> *snip*
>
> [process list]
> o yum-3215
> device cached added removed indirect
> (maj:min) inode pages pages pages removed pages
> ----------------------------------------------------------------
> 253:0 16 34130 5752 0 0
> 253:0 198 9463 2233 0 0
> 253:0 639 628 51 0 0
> 253:0 778 29 78 0 0
> 253:0 7305 49005 12307 0 0
> 253:0 144217 10 11 0 0
> 253:0 262775 13 39 0 0
> *snip*
> ----------------------------------------------------------------
> total: 102346 26165 1 0
^^^
Is this 1 stray?
>
> We can now know system-wide pagecache usage by /proc/meminfo.
> But we have no method to get higher resolution information like per file or
> per process usage than system-wide one.
It would be really nice to see if we can detect the mapped from the
unmapped page cache
> A process may share some pagecache or add a pagecache to the memory or
> remove a pagecache from the memory.
> If a pagecache miss hit ratio rises, maybe it leads to extra I/O and
> affects system performance.
>
> So, by using the tracepoints we can get the following information.
> 1. how many pagecaches each process has per each file
> 2. how many pages are cached per each file
> 3. how many pagecaches each process shares
> 4. how often each process adds/removes pagecache
> 5. how long a pagecache stays in the memory
> 6. pagecache hit rate per file
>
> Especially, the monitoring pagecache usage per each file and pagecache hit
> ratio would help us tune some applications like database.
> And it will also help us tune the kernel parameters like "vm.dirty_*".
>
> Changelog since v2
> o add new script to monitor pagecache hit ratio per process.
> o use DECLARE_EVENT_CLASS
>
> Changelog since v1
> o Add a script based on "perf trace stream scripting support".
>
> Any comments are welcome.
--
Three Cheers,
Balbir
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