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

[Zhitao Li]

Hello, Amar,


It still fails in quorum test.

The root inode resolution succeeds, and stat is called. It fails because of quorum check in afr translator.



Sincerely,
Zhitao
________________________________
From: Amar Tumballi <atumball at redhat.com>
Sent: Friday, March 24, 2017 10:24:53 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?

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

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