linux-kernel - Re: Linux 2.6.29

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]

Date:	Sat, 4 Apr 2009 00:32:18 +0200
From:	Janne Grunau <j@...nau.net>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Mark Lord <lkml@....ca>,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>, tytso@....edu,
	drees76@...il.com, jesper@...gh.cc,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Fri, Apr 03, 2009 at 05:57:05PM -0400, Jeff Garzik wrote:
> Janne Grunau wrote:
> > On Fri, Apr 03, 2009 at 03:57:52PM -0400, Jeff Garzik wrote:
> >> mythtv/libs/libmythtv/ThreadedFileWriter.cpp is a good place to start 
> >> (Sync method... uses fdatasync if available, fsync if not).
> >>
> >> mythtv is definitely a candidate for sync_file_range() style output, IMO.
> 
> > yeah, I'm on it.
> 
> Just curious, does MythTV need fsync(), or merely to tell the kernel to 
> begin asynchronously writing data to storage?

quoting the TheadedFileWriter comments

/*
 *   NOTE: This doesn't even try flush our queue of data.
 *   This only ensures that data which has already been sent
 *   to the kernel for this file is written to disk. This 
 *   means that if this backend is writing the data over a 
 *   network filesystem like NFS, then the data will be visible
 *   to the NFS server after this is called. It is also useful
 *   in preventing the kernel from buffering up so many writes
 *   that they steal the CPU for a long time when the write
 *   to disk actually occurs.
 */
 
> sync_file_range(..., SYNC_FILE_RANGE_WRITE) might be enough, if you do 
> not need to actually wait for completion.
>
> This may be the case, if the idea behind MythTV's fsync(2) is simply to 
> prevent the kernel from building up a huge amount of dirty pages in the 
> pagecache [which, in turn, produces bursty write-out behavior].

see above, we care only about the write-out. The f{data}*sync calls are
already in a seperate thread doing nothing else.

Janne
--
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/