On Wed, Sep 9, 2015 at 5:34 PM, Gregory Farnum <gfarnum@xxxxxxxxxx> wrote:
> On Wed, Sep 9, 2015 at 3:27 PM, Kyle Hutson <kylehutson@xxxxxxx> wrote:
>> We are using Hammer - latest released version. How do I check if it's
>> getting promoted into the cache?
>
> Umm...that's a good question. You can run rados ls on the cache pool,
> but that's not exactly scalable; you can turn up logging and dig into
> them to see if redirects are happening, or watch the OSD operations
> happening via the admin socket. But I don't know if there's a good
> interface for users to just query the cache state of a single object.
> :/
>
>>
>> We're using the latest ceph kernel client. Where do I poke at readahead
>> settings there?
>
> Just the standard kernel readahead settings; I'm not actually familiar
> with how to configure those but I don't believe Ceph's are in any way
> special. What do you mean by "latest ceph kernel client"; are you
> running one of the developer testing kernels or something? I think
> Ilya might have mentioned some issues with readahead being
> artificially blocked, but that might have only been with RBD.
That's a system wide issue - it affects md folks and generally
everybody who can benefit from a large readahead window. Notes from
the perf etherpad:
- kernel page cache readahead is capped at 2M since 3.15, that patch
was backported so older kernels (e.g. 3.14.21+) are affected as well
- Red Hat and Oracle seem to be shipping a patch that effectively
reverts this, but someone needs to check that
- a patch that gets rid of this limit is in the works, Linus seems to
be happy with it, expect it in 4.3 or 4.4?
Thanks,
Ilya
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