[Gluster-devel] Could we not always call lookup for root_dir in fuse_getattr to improve performance?

[Amar Tumballi]

Test this patch https://review.gluster.org/#/c/16945/

On Fri, Mar 24, 2017 at 9:42 AM, Zhitao Li <zhitaoli1201 at outlook.com> wrote:

> Dear Amar,
>
>
> Thanks very much for your kind help!
>
>
>
> I have seen the patch you submit.
>
>
> I disable the check and do regression test locally. It indeed *brings a
> bug in "tests/basic/afr/quorum.t"*(for tests/ec/, there exists failure
> but it is hard to reappear the failure).
>
>
> For quorum test, it fails  in line_no 36. The case is that for a volume
> with replica 2, a brick is killed and quorum-reads is on, quorum-type is
> fixed. Stat on the root_dir will fail because of quorum
> check(afr/afr-read-txn.c). However, lookup will succeed without
> quorum check. This is what I have got.
>
> So the solution maybe more complex than removing the nodeid==1 check
> directly.
>
>
> Thank you!
>
> Best regards,
> Zhitao Li
> ------------------------------
> *From:* Amar Tumballi <atumball at redhat.com>
> *Sent:* Friday, March 24, 2017 9:13:35 PM
> *To:* Zhitao Li
> *Cc:* Niels de Vos; Poornima Gurusiddaiah; Gluster Devel;
> gluster-users at gluster.org; Zhitao Li; Zhitao Li
> *Subject:* Re: Could we not always call lookup for root_dir in
> fuse_getattr to improve performance?
>
> Went through the code base again. Yes, as you said, we can get rid of
> fuse_getattr() not checking nodeid==1 path.
>
> Patch here:  https://review.gluster.org/16944
>
> -Amar
>
>
>
> On Fri, Mar 24, 2017 at 2:57 AM, Zhitao Li <zhitaoli1201 at outlook.com>
> wrote:
>
>> Hello, everyone!
>>
>>
>> I am now optimizing the performance of "ls". When there are many little
>> files directly in mount point(root dir of glusterfs), I find that
>> fuse_getattr takes near half time of total "ls". Strictly, the nodeid==1
>> check in fuse_getattr will call look operation instead of stat, and lookup
>> will always miss the md-cache, so it will do real lookup and cost about 3ms
>> a time in my case.
>>
>>
>> I doubt whether the special check of nodeid==1 is necessary. I disable
>> the check,  it works normal for ls. However, in the "tests" of gluster, it
>> fails(quorum.t). In that case, lookup in root_dir is essential.
>>
>>
>> Up to now, we know that lookup bring high cost in fuse_getattr and it is
>> essential in some case. Could anyone give some advice to improve
>> fuse_getattr(lookup in root_dir) without bringing bugs?
>>
>>
>> I have been trying to deal  with this for many days. Your help is greatly
>> in need.
>>
>>
>>
>> Best regards,
>> Zhitao Li
>>
>
>
>
> --
> Amar Tumballi (amarts)
>



-- 
Amar Tumballi (amarts)
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