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SubjectRe: + zram-support-compaction.patch added to -mm tree
On (03/09/15 10:05), Minchan Kim wrote:
> > well, to be fair, compaction is a zsmalloc internal. zram has nothing to do with
> > it.
> >
> > but do we we even need this stat? it seems that
> >
> > mem_total_used (before compaction) - mem_total_user (after comapction)
> >
> > will give user an idea on how much memory was compacted.
>
> It's not enough. What I want to know is compaction efficiency per client of
> zsmalloc(ie, zram).
>

so what a typical user can do with this information? isn't it an entirely
debug info that makes some hidden sense only to developers?

if you insist on exporting this as a zram stat for everyone how obout
starting to move away from per-stat RO sysfs attrs. it seems that we have
uncomfortably a lot of sysfs attrs, and that doesn't make life easier in
user space. for example, block devices have /sys/block/.../stat file:

/sys/block/sda$ cat stat
45931 59 2075686 289906 55768 9229 1967800 318033 0 193583 607806

and there are no num_reads, num_writes, num_failed_reads, num_failed_writes,
etc., etc. per-stat sysfs attrs force user-space to do lots of syscalls:
open(), read(), close() with error control on every step; for every stat.

so how about introducing zram<id>/malloc_stats (or any similar name) and
provide compaction and all future allocator related stats there
(via s*printf("%d %d %d", ....)) ?

-ss

> IOW, (how many of freed pages / how many of objects) per
> zs_compact.
>
> >
> > -ss
> >
> > > That's why it is on debugfs. If we add the stat into zsmalloc, we should turn on debugfs
> > > and CONFIG_ZSMALLOC_STAT to see *a* stat. Even, CONFIG_ZSMALLOC_STAT will add
> > > unncessary overheads to account another stats fo zsmalloc internals.
> > >
> > > As well, if we add auto-compacion like stuff in zsmalloc(ie, it will trigger
> > > by itself if fragmention is over to predefined theshold), the stat will
> > > accumulate stat while someone want to see snapshot compaction effiecieny
> > > of the moment.
> > >
> > > So, I want to keep it in zram now.
> > >
> > > --
> > > Kind regards,
> > > Minchan Kim
> > >
>
> --
> Kind regards,
> Minchan Kim
>


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