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From: Blair Bethwaite <blair.bethwaite-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Kyle Bader <kyle.bader-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: "ceph-users-idqoXFIVOFJgJs9I8MT0rw@public.gmane.org"
	<ceph-users-idqoXFIVOFJgJs9I8MT0rw@public.gmane.org>,
	Ceph Development
	<ceph-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: Dramatic performance drop at certain number of objects in pool
Date: Mon, 27 Jun 2016 18:12:38 +1000	[thread overview]
Message-ID: <CA+z5DswEaFJsr6uykeYF488is9XMwvwNpPMUC1QXvfdvp9sJcg@mail.gmail.com> (raw)
In-Reply-To: <CAFMfnwoqbr+_c913oyxpvzHNS+NPdXX17dMdXoC1ZiuZM1GzPw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


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On 25 Jun 2016 6:02 PM, "Kyle Bader" <kyle.bader-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> fdatasync takes longer when you have more inodes in the slab caches, it's
the double edged sword of vfs_cache_pressure.

That's a bit sad when, iiuc, it's only journals doing fdatasync in the Ceph
write path. I'd have expected the vfs to handle this on a per fs basis (and
a journal filesystem would have very little in the inode cache).

It's somewhat annoying there isn't a way to favor dentries (and perhaps
dentry inodes) over other inodes in the vfs cache. Our experience shows
that it's dentry misses that cause the major performance issues (makes
sense when you consider the osd is storing all its data in the leafs of the
on disk PG structure).

This is another discussion that seems to backup the choice to implement
bluestore.

Cheers,
Blair

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  parent reply	other threads:[~2016-06-27  8:12 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-16 12:14 Dramatic performance drop at certain number of objects in pool Wade Holler
2016-06-16 12:48 ` Blair Bethwaite
     [not found]   ` <CA+z5Dsz=e1N9RxRoF5Wao8Dogf_S1UstNZaCJ=oj-efj83HBig-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-16 14:20     ` Dramatic performance drop at certain number ofobjects " Mykola
2016-06-16 14:30     ` Dramatic performance drop at certain number of objects " Wade Holler
2016-06-16 14:32     ` Wade Holler
2016-06-16 13:38 ` Wido den Hollander
2016-06-16 14:47   ` Wade Holler
2016-06-16 16:08     ` Wade Holler
2016-06-17  8:49       ` Wido den Hollander
2016-06-19 23:21   ` Blair Bethwaite
     [not found]     ` <CA+z5DszqHuevkAF3W01R=7AAeqVcyuHZTX0+bAvThgihvOjwuA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-20  0:52       ` Christian Balzer
2016-06-20  6:32     ` Blair Bethwaite
     [not found]       ` <CA+z5Dsy4tbyiL71C8CQCTQ66tY1=9thSWdNA4BSn6=tNfGUE6w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-20 18:48         ` Wade Holler
     [not found]           ` <CA+e22Sc3iY5Lvp4oGwJ_wwpJsOJsWdB1thaHWEAuYP=bbGHAeg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-20 20:47             ` Warren Wang - ISD
     [not found]               ` <D38DCB57.131AE%warren.wang-dFwxUrggiyBBDgjK7y7TUQ@public.gmane.org>
2016-06-20 22:58                 ` Christian Balzer
2016-06-23  1:26                   ` [ceph-users] " Wade Holler
     [not found]                     ` <CA+e22SdrwRHmAD=67MpVtUXVyCOmidcoUXrANZVeDJc2tcJfnQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-23  1:33                       ` Blair Bethwaite
2016-06-23  1:41                         ` [ceph-users] " Wade Holler
2016-06-23  2:01                           ` Blair Bethwaite
2016-06-23  2:28                             ` Christian Balzer
2016-06-23  2:36                               ` Blair Bethwaite
2016-06-23  2:31                             ` Wade Holler
     [not found]                           ` <CA+e22SfaiBUQ9Wanay6_oji9t7131o67B2oDtaEW_zXwqCJfbQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-23 22:09                             ` Warren Wang - ISD
     [not found]                               ` <D391D1A4.145D6%warren.wang-dFwxUrggiyBBDgjK7y7TUQ@public.gmane.org>
2016-06-23 22:24                                 ` Somnath Roy
     [not found]                                   ` <BL2PR02MB2115BD5C173011A0CB92F964F42D0-TNqo25UYn65rzea/mugEKanrV9Ap65cLvxpqHgZTriW3zl9H0oFU5g@public.gmane.org>
2016-06-24  0:08                                     ` Christian Balzer
     [not found]                                       ` <20160624090806.1246b1ff-9yhXNL7Kh0lSCLKNlHTxZM8NsWr+9BEh@public.gmane.org>
2016-06-24  0:09                                         ` Somnath Roy
2016-06-24 14:23                                           ` [ceph-users] " Wade Holler
     [not found]                                             ` <CA+e22SdmGJVzJX9+63T41UGsfFcxs9R=xZqniQyTgu-yG=h0cA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-24 16:24                                               ` Warren Wang - ISD
     [not found]                                                 ` <D392D6EB.146C6%warren.wang-dFwxUrggiyBBDgjK7y7TUQ@public.gmane.org>
2016-06-24 19:45                                                   ` Wade Holler
2016-06-25  3:07                                                     ` [ceph-users] " Christian Balzer
     [not found]                                             ` <CAFMfnwoqbr+_c913oyxpvzHNS+NPdXX17dMdXoC1ZiuZM1GzPw@mail.gmail.com>
     [not found]                                               ` <CAFMfnwoqbr+_c913oyxpvzHNS+NPdXX17dMdXoC1ZiuZM1GzPw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-27  8:12                                                 ` Blair Bethwaite [this message]
2016-06-23  2:37                         ` Christian Balzer
     [not found]                           ` <20160623113717.446a1f9d-9yhXNL7Kh0lSCLKNlHTxZM8NsWr+9BEh@public.gmane.org>
2016-06-23  2:55                             ` Blair Bethwaite
     [not found]                               ` <CA+z5DszcLqV32NnWeuu+WsRZoZwM493Jfy7WcSpVtaDyArwFAQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-06-23  3:38                                 ` Christian Balzer

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