linux-kernel - Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK

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:	Fri, 22 Apr 2011 16:33:11 -0700
From:	Sunil Mushran <sunil.mushran@...cle.com>
To:	Andreas Dilger <adilger@...ger.ca>
CC:	Eric Blake <eblake@...hat.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Christoph Hellwig <hch@...radead.org>,
	Josef Bacik <josef@...icpanda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK_DATA flags

On 04/22/2011 11:06 AM, Andreas Dilger wrote:
> Sure, there are lots of wasted syscalls, but in this case the cost of doing extra SEEK_DATA and SEEK_HOLE operations may be fairly costly. This involves scanning the whole disk layout, possibly over a network, which might need tens or hundreds of disk seeks to read the metadata, unlike regular SEEK_SET.
>
> Even SEEK_END is somewhat costly on a network filesystem, since the syscall needs to lock the file size in order to determine the end of the file, which can block other threads from writing to the file.
>
> So while I agree that the Linux mantra that "syscalls are cheap" is true if those syscalls don't actually do any work, I think it also ignores the cost of what some syscalls need to do behind the scenes.

You have a point. I was just reviewing the possible patch for ocfs2
and it looks heavy.

One option is to scrap SEEK_* and make another syscall llfind() with FIND_*.
Or, do both.
--
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/