linux-kernel - Re: [RFC] mmaped copy too slow?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Thu, 17 Jan 2008 12:23:16 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Paulo Marques <pmarques@...popie.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] mmaped copy too slow?

Hi

> > One thing you could also try is to pass MAP_POPULATE to mmap so that the 
> > page tables are filled in at the time of the mmap, avoiding a lot of 
> > page faults later.
> > 
> 
> OK, I will test your idea and report about tomorrow.
> but I don't think page fault is major performance impact.

I got more interesting result :)
MAP_POPULATE is harmful result at large copy.


1G copy
                             elapse(sec)
--------------------------------------------
mmap                          71.54
mmap + madvice                69.63
mmap + populate              100.87
mmap + populate + madvice    101.16


more detail:
time command output of mmap copy
	0.50user 3.59system 1:11.54elapsed 5%CPU (0avgtext+0avgdata 0maxresident)k
	2101192inputs+2097160outputs (32776major+491573minor)pagefaults 0swaps

time command output of mmap+populate copy
	0.53user 5.13system 1:40.87elapsed 5%CPU (0avgtext+0avgdata 0maxresident)k
	4200808inputs+2097160outputs (49164major+737340minor)pagefaults 0swaps


input blocks increase about x2.
in fact, mmap(MAP_POPULATE) read disk to memory and drop it just after,
thus read again. 


of cource, when copy file size is enough small, MAP_POPULATE is effective.


100M copy
                             elapse(sec)
--------------------------------------------
mmap                          7.38
mmap + madvice                7.29
mmap + populate               7.13
mmap + populate + madvice     6.65


- kosaki


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/