linux-ext4 - Re: [ext3][kernels >= 2.6.20.7 at least] KDE going comatose when FS is under heavy write load (massive starvation)

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

Message-ID: <46C49556.4000409@clusterfs.com>
Date:	Thu, 16 Aug 2007 22:20:06 +0400
From:	Alex Tomas <alex@...sterfs.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [ext3][kernels >= 2.6.20.7 at least] KDE going comatose when
 FS is under heavy write load (massive starvation)

Andrew Morton wrote:
>>> But under this proposal, t_sync_datalist just gets removed: the new
>>> ordered-data mode _only_ need to do the sb->inode->page walk.  So if I'm
>>> understanding you, the way in which we'd handle any such race is to make
>>> kjournald's writeback of the dirty pages block in lock_page().  Once it
>>> gets the page lock it can look to see if some other thread has mapped the
>>> page to disk.
>> if I'm right holding number of pages locked, then they won't be locked, but
>> writeback. of course kjournald can block on writeback as well, but how does
>> it find pages with *newly allocated* blocks only?
> 
> I don't think we'd want kjournald to do that.  Even if a page was dirtied
> by an overwrite, we'd want to write it back during commit, just from a
> quality-of-implementation point of view.  If we were to leave these pages
> unwritten during commit then a post-recovery file could have a mix of
> up-to-five-second-old data and up-to-30-seconds-old data.

trying to implement this I've got to think that there is one significant
difference between t_sync_datalist and sb->inode->page walk: t_sync_datalist
is per-transaction. IOW, it doesn't change once transaction is closed. in
contrast, nothing (currently) would prevent others to modify pages while
commit is in progress. I think this is serious disadvantage of the solution.

what I'd propose is sort of in-core tracker for all data-related IOs in flight
(assigned to specific transaction) and wait for their completion in commit
thread.

thanks, Alex


-
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