linux-kernel - mmap_sem contention issues

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>] [day] [month] [year] [list]

Message-ID: <CALCETrW=0gQMBW=nLKCWS-O7H5q6zYFCbFGOcC2PTS668=Z_NA@mail.gmail.com>
Date:	Mon, 26 Nov 2012 12:12:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: mmap_sem contention issues

I'm having serious latency problems due to mmap_sem contention.  I
have a real-time thread that has (soft) page faults on locked pages,
and it blocks for multiple milliseconds on
(call_rwsem_down_read_failed do_page_fault page_fault).  Can this be
fixed?

Some ideas:

1. Drop mmap_sem during the filesystem part of mmap and munmap.
(MAP_POPULATE in particular is a disaster -- using it will easily
increase latency from a few milliseconds to a respectable fraction of
a second.)

2. Come up with some way to lock specific vm_area_structs for read
access without taking mmap_sem at all.  This looks unpleasant with the
current rbtree structure -- something like a radix tree might work
much better if the nodes were to contain their own locks.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
--
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/