From: miquels@cistron-office.nl (Miquel van Smoorenburg)
To: linux-kernel@vger.kernel.org
Subject: Re: O_DIRECT! or O_DIRECT?
Date: Wed, 4 Jul 2001 20:23:10 +0000 (UTC) [thread overview]
Message-ID: <9hvtvd$9o2$1@ncc1701.cistron.net> (raw)
In-Reply-To: <E15HWsV-0000lM-00@f12.port.ru> <20010704185230.F28793@redhat.com> <9hvn61$rkb$1@ncc1701.cistron.net> <20010704193402.A6403@redhat.com>
In article <20010704193402.A6403@redhat.com>,
Stephen C. Tweedie <sct@redhat.com> wrote:
>Hi,
>
>On Wed, Jul 04, 2001 at 06:27:13PM +0000, Miquel van Smoorenburg wrote:
>>
>> Any chance of something like O_SEQUENTIAL (like madvise(MADV_SEQUENTIAL))
>
>What for? The kernel already optimises readahead and writebehind for
>sequential files.
Yes, but I really do mean like in madvise().
>If you want to provide specific extra hints to the kernel, then things
>like O_UNCACHE might be more appropriate to instruct the kernel to
>explicitly remove the cached page after IO completes (to avoid the VM
>overhead of maintaining useless cache). That would provide a definite
>improvement over normal IO for large multimedia-style files or for
>huge copies. But what part of the normal handling of sequential files
>would O_SEQUENTIAL change? Good handling of sequential files should
>be the default, not an explicitly-requested feature.
exactly what I meant, since that is what MADV_SEQUENTIAL seems to do:
linux/mm/filemap.c:
* MADV_SEQUENTIAL - pages in the given range will probably be accessed
* once, so they can be aggressively read ahead, and
* can be freed soon after they are accessed.
/*
* Read-ahead and flush behind for MADV_SEQUENTIAL areas. Since we are
* sure this is sequential access, we don't need a flexible read-ahead
* window size -- we can always use a large fixed size window.
*/
static void nopage_sequential_readahead(struct vm_area_struct * vma,
O_SEQUENTIAL perhaps is the wrong name.
I'd like to see this so I can run tar to backup a machine during the
day (if tar used this flag, ofcourse) without performance going
down the drain because of cache pollution.
Mike.
next prev parent reply other threads:[~2001-07-04 20:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-03 20:34 O_DIRECT! or O_DIRECT? Samium Gromoff
2001-07-03 20:38 ` kernel
2001-07-03 21:12 ` Anton Altaparmakov
2001-07-04 17:52 ` Stephen C. Tweedie
2001-07-04 18:27 ` Miquel van Smoorenburg
2001-07-04 18:34 ` Stephen C. Tweedie
2001-07-04 20:23 ` Miquel van Smoorenburg [this message]
2001-07-05 15:06 ` Stephen C. Tweedie
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='9hvtvd$9o2$1@ncc1701.cistron.net' \
--to=miquels@cistron-office.nl \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).