[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Thu, 08 Aug 2013 15:58:39 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Andy Lutomirski <luto@...capital.net>
CC: Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/3] Add madvise(..., MADV_WILLWRITE)
I was coincidentally tracking down what I thought was a scalability
problem (turned out to be full disks :). I noticed, though, that ext4
is about 20% slower than ext2/3 at doing write page faults (x-axis is
number of tasks):
http://www.sr71.net/~dave/intel/page-fault-exts/cmp.html?1=ext3&2=ext4&hide=linear,threads,threads_idle,processes_idle&rollPeriod=5
The test case is:
https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault3.c
A 'perf diff' shows some of the same suspects that you've been talking
about, Andy:
http://www.sr71.net/~dave/intel/page-fault-exts/diffprofile.txt
> 2.39% +2.34% [kernel.kallsyms] [k] __set_page_dirty_buffers
> +2.50% [kernel.kallsyms] [k] __block_write_begin
> +2.16% [kernel.kallsyms] [k] __block_commit_write
The same test on ext4 but doing MAP_PRIVATE instead of MAP_SHARED goes
at the same speed as ext2/3:
https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault2.c
This is looking to me more like an ext4-specific problem that needs to
get solved rather than through some interfaces (like MADV_WILLWRITE).
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists