From: Linus Torvalds <torvalds@transmeta.com>
To: riel@nl.linux.org
Cc: Andrea Arcangeli <andrea@suse.de>,
Kanoj Sarcar <kanoj@google.engr.sgi.com>,
Ben LaHaise <bcrl@redhat.com>,
linux-mm@kvack.org
Subject: Re: [patch] take 2 Re: PG_swap_entry bug in recent kernels
Date: Sat, 22 Apr 2000 12:58:17 -0700 (PDT) [thread overview]
Message-ID: <Pine.LNX.4.10.10004221254100.1014-100000@penguin.transmeta.com> (raw)
In-Reply-To: <Pine.LNX.4.21.0004221520310.16974-100000@duckman.conectiva>
On Sat, 22 Apr 2000, Rik van Riel wrote:
>
> It all depends on the source code. If we're holding the page
> lock anyway in places where we play with the other flags, that's
> probably the best strategy, but if we're updating the page flags
> in a lot of places without holding the page lock, then it's
> probably better to just do everything with the current atomic
> bitops.
I suspect that we hold the page lock already. And it just seems wrong that
we could ever alter some of the flags (like dirty or uptodate) without
holding the page lock. So the logic is more than just "bitfield
coherency": it's also a higher-level coherency guarantee.
> Btw, here's a result from 2.3.99-pre6-3 ... line number 3 and
> 4 are extremely suspect...
>
> [riel@duckman mm]$ grep 'page->flags' *.c
> filemap.c: if (test_and_clear_bit(PG_referenced, &page->flags))
> filemap.c: set_bit(PG_referenced, &page->flags);
> filemap.c: flags = page->flags & ~((1 << PG_uptodate) | (1 << PG_error) | (1 << PG_dirty));
> filemap.c: page->flags = flags | (1 << PG_locked) | (1 << PG_referenced);
Both 3 and 4 are from the same sequence: it's the initialization code for
the page. They are run before the page is added to the page cache, so
atomicity is not even an issue, because nobody can get at the page
beforeit ison any of the page lists. Think of it as an anonymous page that
is just about to get truly instantiated into the page cache.
It's also one of the few timeswhere we truly touch many bits. In most
other caseswe touch just one or two at a time.
Linus
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux.eu.org/Linux-MM/
next prev parent reply other threads:[~2000-04-22 19:58 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-04-03 22:22 PG_swap_entry bug in recent kernels Ben LaHaise
2000-04-04 15:06 ` Andrea Arcangeli
2000-04-04 15:46 ` Rik van Riel
2000-04-04 16:50 ` Andrea Arcangeli
2000-04-04 17:06 ` Ben LaHaise
2000-04-04 18:03 ` Andrea Arcangeli
2000-04-06 22:11 ` [patch] take 2 " Ben LaHaise
2000-04-07 10:45 ` Andrea Arcangeli
2000-04-07 11:29 ` Rik van Riel
2000-04-07 12:00 ` Andrea Arcangeli
2000-04-07 12:54 ` Rik van Riel
2000-04-07 13:14 ` Andrea Arcangeli
2000-04-07 20:12 ` Kanoj Sarcar
2000-04-07 23:26 ` Andrea Arcangeli
2000-04-08 0:11 ` Kanoj Sarcar
2000-04-08 0:37 ` Kanoj Sarcar
2000-04-08 13:20 ` Andrea Arcangeli
2000-04-08 21:39 ` Kanoj Sarcar
2000-04-08 23:02 ` Andrea Arcangeli
2000-04-08 23:18 ` Kanoj Sarcar
2000-04-08 23:58 ` Andrea Arcangeli
2000-04-08 13:30 ` Andrea Arcangeli
2000-04-08 17:39 ` Andrea Arcangeli
2000-04-07 23:54 ` Andrea Arcangeli
2000-04-08 0:15 ` Kanoj Sarcar
2000-04-08 13:14 ` Andrea Arcangeli
2000-04-08 21:47 ` Kanoj Sarcar
2000-04-08 23:10 ` Andrea Arcangeli
2000-04-08 23:21 ` Kanoj Sarcar
2000-04-08 23:39 ` Andrea Arcangeli
2000-04-09 0:40 ` Kanoj Sarcar
2000-04-10 8:55 ` andrea
2000-04-11 2:45 ` Kanoj Sarcar
2000-04-11 16:22 ` Andrea Arcangeli
2000-04-11 17:40 ` Rik van Riel
2000-04-11 18:20 ` Kanoj Sarcar
2000-04-21 18:23 ` Andrea Arcangeli
2000-04-21 21:00 ` Rik van Riel
2000-04-22 1:12 ` Andrea Arcangeli
2000-04-22 1:51 ` Linus Torvalds
2000-04-22 18:29 ` Rik van Riel
2000-04-22 19:58 ` Linus Torvalds [this message]
2000-04-11 18:26 ` Kanoj Sarcar
2000-04-10 19:10 ` Stephen C. Tweedie
2000-04-08 0:04 ` Andrea Arcangeli
[not found] <yttem7xstk2.fsf@vexeta.dc.fi.udc.es>
2000-04-23 0:52 ` Andrea Arcangeli
[not found] <yttk8ho26s8.fsf@vexeta.dc.fi.udc.es>
2000-04-23 16:07 ` Andrea Arcangeli
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=Pine.LNX.4.10.10004221254100.1014-100000@penguin.transmeta.com \
--to=torvalds@transmeta.com \
--cc=andrea@suse.de \
--cc=bcrl@redhat.com \
--cc=kanoj@google.engr.sgi.com \
--cc=linux-mm@kvack.org \
--cc=riel@nl.linux.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.