linux-kernel - Re: [PATCH v5 4/6] mm, proc: reduce cost of /proc/pid/smaps for unpopulated shmem mappings

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20151119101333.GC8494@dhcp22.suse.cz>
Date:	Thu, 19 Nov 2015 11:13:33 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Jerome Marchand <jmarchan@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Subject: Re: [PATCH v5 4/6] mm, proc: reduce cost of /proc/pid/smaps for
 unpopulated shmem mappings

On Wed 18-11-15 10:29:34, Vlastimil Babka wrote:
> Following the previous patch, further reduction of /proc/pid/smaps cost is
> possible for private writable shmem mappings with unpopulated areas where
> the page walk invokes the .pte_hole function. We can use radix tree iterator
> for each such area instead of calling find_get_entry() in a loop. This is
> possible at the extra maintenance cost of introducing another shmem function
> shmem_partial_swap_usage().
> 
> To demonstrate the diference, I have measured this on a process that creates a
> private writable 2GB mapping of a partially swapped out /dev/shm/file (which
> cannot employ the optimizations from the prvious patch) and doesn't populate it
> at all. I time how long does it take to cat /proc/pid/smaps of this process 100
> times.
> 
> Before this patch:
> 
> real    0m3.831s
> user    0m0.180s
> sys     0m3.212s
> 
> After this patch:
> 
> real    0m1.176s
> user    0m0.180s
> sys     0m0.684s
> 
> The time is similar to case where radix tree iterator is employed on the whole
> mapping.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Looks good as well.
Acked-by: Michal Hocko <mhocko@...e.com>
[...]
-- 
Michal Hocko
SUSE Labs
--
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/