linux-kernel - Re: [RFC PATCH] mm, compaction: allow compaction for GFP

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Message-ID: <20161018062446.GD14023@dastard>
Date:   Tue, 18 Oct 2016 17:24:46 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <js1304@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm, compaction: allow compaction for GFP_NOFS
 requests

On Mon, Oct 17, 2016 at 10:22:56AM +0200, Michal Hocko wrote:
> On Mon 17-10-16 07:49:59, Dave Chinner wrote:
> > On Thu, Oct 13, 2016 at 01:04:56PM +0200, Michal Hocko wrote:
> > > On Thu 13-10-16 09:39:47, Michal Hocko wrote:
> > > > On Thu 13-10-16 11:29:24, Dave Chinner wrote:
> > > > > On Fri, Oct 07, 2016 at 03:18:14PM +0200, Michal Hocko wrote:
> > > > [...]
> > > > > > Unpatched kernel:
> > > > > > #       Version 3.3, 16 thread(s) starting at Fri Oct  7 09:55:05 2016
> > > > > > #       Sync method: NO SYNC: Test does not issue sync() or fsync() calls.
> > > > > > #       Directories:  Time based hash between directories across 10000 subdirectories with 180 seconds per subdirectory.
> > > > > > #       File names: 40 bytes long, (16 initial bytes of time stamp with 24 random bytes at end of name)
> > > > > > #       Files info: size 0 bytes, written with an IO size of 16384 bytes per write
> > > > > > #       App overhead is time in microseconds spent in the test not doing file writing related system calls.
> > > > > > #
> > > > > > FSUse%        Count         Size    Files/sec     App Overhead
> > > > > >      1      1600000            0       4300.1         20745838
> > > > > >      3      3200000            0       4239.9         23849857
> > > > > >      5      4800000            0       4243.4         25939543
> > > > > >      6      6400000            0       4248.4         19514050
> > > > > >      8      8000000            0       4262.1         20796169
> > > > > >      9      9600000            0       4257.6         21288675
> > > > > >     11     11200000            0       4259.7         19375120
> > > > > >     13     12800000            0       4220.7         22734141
> > > > > >     14     14400000            0       4238.5         31936458
> > > > > >     16     16000000            0       4231.5         23409901
> > > > > >     18     17600000            0       4045.3         23577700
> > > > > >     19     19200000            0       2783.4         58299526
> > > > > >     21     20800000            0       2678.2         40616302
> > > > > >     23     22400000            0       2693.5         83973996
> > > > > > Ctrl+C because it just took too long.
> > > > > 
> > > > > Try running it on a larger filesystem, or configure the fs with more
> > > > > AGs and a larger log (i.e. mkfs.xfs -f -dagcount=24 -l size=512m
> > > > > <dev>). That will speed up modifications and increase concurrency.
> > > > > This test should be able to run 5-10x faster than this (it
> > > > > sustains 55,000 files/s @ 300MB/s write on my test fs on a cheap
> > > > > SSD).
> > > > 
> > > > Will add more memory to the machine. Will report back on that.
> > > 
> > > increasing the memory to 1G didn't help. So I've tried to add
> > > -dagcount=24 -l size=512m and that didn't help much either. I am at 5k
> > > files/s so nowhere close to your 55k. I thought this is more about CPUs
> > > count than about the amount of memory. So I've tried a larger machine
> > > with 24 CPUs (no dagcount etc...), this one doesn't have a fast storage
> > > so I've backed the fs image by ramdisk but even then I am getting very
> > > similar results. No idea what is wrong with my kvm setup.
> > 
> > What's the backing storage? I use an image file in an XFS
> > filesystem, configured with virtio,cache=none so it's concurrency
> > model matches that of a real disk...
> 
> I am using qcow qemu image exported to qemu by
> -drive file=storage.img,if=ide,index=1,cache=none
> parameter.

storage.img is on what type of filesystem? Only XFs will give you
proper IO concurrency with direct IO, and you really need to use a
raw image file rather than qcow2. If you're not using the special
capabilities of qcow2 (e.g. snapshots), there's no reason to use
it...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com