[Bugs] [Bug 1437780] New: don't send lookup in fuse_getattr()

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1437780

            Bug ID: 1437780
           Summary: don't send lookup in fuse_getattr()
           Product: GlusterFS
           Version: mainline
         Component: fuse
          Severity: medium
          Assignee: bugs at gluster.org
          Reporter: atumball at redhat.com
                CC: bugs at gluster.org



Description of problem:
Fuse getattr() sends root_lookup() in case of nodeid == 1, instead of sending
stat() itself.

Additional info:
Copy of the mail thread:

-----


    On Fri, Mar 24, 2017 at 8:12 PM, Zhitao Li zhitaoli1201 at outlook.com wrote:

    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. 

        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>
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.

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