From: Andrea Arcangeli <andrea@suse.de>
To: Andrew Morton <akpm@osdl.org>
Cc: nickpiggin@yahoo.com.au, riel@redhat.com,
marcelo.tosatti@cyclades.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][5/?] count writeback pages in nr_scanned
Date: Thu, 6 Jan 2005 06:59:05 +0100 [thread overview]
Message-ID: <20050106055905.GT4597@dualathlon.random> (raw)
In-Reply-To: <20050105213704.0282316f.akpm@osdl.org>
On Wed, Jan 05, 2005 at 09:37:04PM -0800, Andrew Morton wrote:
> Andrea Arcangeli <andrea@suse.de> wrote:
> >
> > 2) we won't need unreliable anti-deadlock timeouts anymore
>
> The timeouts are for:
>
> a) A fallback for backing stores which don't wake up waiters in
> blk_congestion_wait() (eg: NFS).
that anti-deadlock will be unnecessary too with the new logic.
> b) handling the race case where the request queue suddenly goes empty
> before the sleeper gets onto the waitqueue.
as I mentioned with proper locking setting task in uninterruptible and
then registering into the new per classzone waitqueue, the timeout will
be unnecessary even for this.
> It can probably be removed with some work, and additional locking.
The additional locking will then remove the current locking in
blk_congestion_wait so it's new locking but it will replace the current
locking. But I agree registering in the waitqueue inside the
blk_congestion_wait was simpler. It's just I've an hard time to like the
timeout. Timeout is always wrong when it triggers: if it triggers it
always triggers either too late (wasted resources) or too early (early
oom kills). So unless it messes everything up, it'd be nice to the
locking strict. anyway point 1 and 2 can be implemented separately, at
first we can leave the timeout if the race is too hard to handle.
Ideally if we keep the total number of oustanding writebacks
per-classzone (not sure if we account for it already somewhere, I guess
if something we've the global number and not the per-classzone one), we
could remove the timeout without having to expose the locking outside
blk_congestion_wait. With the number of oustanding writebacks
per-classzone we could truly fix the race and obsolete the timeout in a
self contained manner. Though it will require a proper amount of memory
barriers around the account increment/decrement/read.
next prev parent reply other threads:[~2005-01-06 5:58 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-03 17:25 [PATCH][5/?] count writeback pages in nr_scanned Rik van Riel
2005-01-05 10:08 ` Andrew Morton
2005-01-05 18:06 ` Andrea Arcangeli
2005-01-05 18:50 ` Rik van Riel
2005-01-05 17:49 ` Marcelo Tosatti
2005-01-05 21:44 ` Andrew Morton
2005-01-05 20:32 ` Marcelo Tosatti
2005-01-05 23:51 ` Nick Piggin
2005-01-06 1:27 ` Rik van Riel
2005-01-06 1:33 ` Nick Piggin
2005-01-06 1:37 ` Andrew Morton
2005-01-06 1:40 ` Nick Piggin
2005-01-06 1:52 ` Andrea Arcangeli
2005-01-06 1:36 ` Andrew Morton
2005-01-06 3:42 ` Rik van Riel
2005-01-06 3:50 ` Nick Piggin
2005-01-06 4:26 ` Andrew Morton
2005-01-06 4:35 ` Nick Piggin
2005-01-06 4:47 ` Andrew Morton
2005-01-06 4:55 ` Nick Piggin
2005-01-06 5:03 ` Andrea Arcangeli
2005-01-06 8:06 ` Jens Axboe
2005-01-06 8:16 ` memory barrier in ll_rw_blk.c (was Re: [PATCH][5/?] count writeback pages in nr_scanned) Nick Piggin
2005-01-06 8:32 ` Jens Axboe
2005-01-06 8:53 ` Nick Piggin
2005-01-06 12:00 ` Jens Axboe
2005-01-06 4:59 ` [PATCH][5/?] count writeback pages in nr_scanned Andrea Arcangeli
2005-01-06 5:05 ` Andrew Morton
2005-01-06 5:17 ` Andrea Arcangeli
2005-01-06 5:19 ` Nick Piggin
2005-01-06 5:25 ` Andrea Arcangeli
2005-01-06 5:36 ` Nick Piggin
2005-01-06 5:44 ` Nick Piggin
2005-01-06 5:37 ` Andrew Morton
2005-01-06 5:59 ` Andrea Arcangeli [this message]
2005-01-06 13:28 ` Rik van Riel
2005-01-06 5:32 ` Andrew Morton
2005-01-06 5:46 ` Andrea Arcangeli
2005-01-06 5:59 ` Andrew Morton
2005-01-06 6:16 ` Andrea Arcangeli
2005-01-06 5:06 ` Nick Piggin
2005-01-06 5:21 ` Andrea Arcangeli
2005-01-05 23:26 ` Andrew Morton
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