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From: Nigel Cunningham <nigel@suspend2.net>
To: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, linux-kernel@vger.kernel.org
Subject: Re: [ 15/23] [Suspend2] Helper for counting uninterruptible threads of a type.
Date: Tue, 31 Jan 2006 15:42:59 +1000	[thread overview]
Message-ID: <200601311543.04302.nigel@suspend2.net> (raw)
In-Reply-To: <20060130222541.GK2250@elf.ucw.cz>

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Hi.

On Tuesday 31 January 2006 08:25, Pavel Machek wrote:
> On Po 30-01-06 23:18:28, Rafael J. Wysocki wrote:
> > Hi,
> >
> > On Thursday 26 January 2006 04:45, Nigel Cunningham wrote:
> > > Add a helper which counts the number of patches of a type (all
> > > or userspace only) which are in TASK_UNINTERRUPTIBLE state.
> > > These tasks are signalled (just in case they leave that state at
> > > a later point), but we do not consider freezing to have failed
> > > if and when they do not enter the freezer.
> > >
> > > Note that when they eventually leave TASK_UNINTERRUPTIBLE state,
> > > they will enter the refrigerator, but will immediately exit if
> > > we no longer want to freeze at that point.
> >
> > I think we need to do something like this to prevent problems with
> > freezing under load.
>
> That is dangerous... task in UNINTERRUPTIBLE may hold some lock,
> AFAICT.
>
> No, there's some simple bug in refrigerator, and I/we need to fix
> that. Signals work under load, so refrigerator should, too.

I know you understand English, Pavel! Re-read what I wrote previously! The 
problem is a race. You're telling processes that process I/O to freeze at the 
same time as you're telling processes that submit I/O to freeze. If kjournald 
(eg) enters the refrigerator while dd is still running, dd is going to have a 
chance of getting stuck, waiting for some I/O to complete.

This also means your sys_sync is totally useless if anything is submitting 
I/O, since there will still be I/O being submitted after the sync is done. 
This is why (in the numbers I submitted yesterday), the current 
implementation took so much longer than the new one. The sys_sync really only 
introduces a big delay. It needs to be done after the things that generate 
I/O have been stopped.

Regards,

Nigel

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  parent reply	other threads:[~2006-01-31  5:46 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-01-26  3:45 [ 00/23] [Suspend2] Freezer Upgrade Patches Nigel Cunningham
2006-01-26  3:45 ` [ 01/23] [Suspend2] Make workqueues freezeable Nigel Cunningham
2006-01-26 23:17   ` Rafael J. Wysocki
2006-01-27  4:01     ` Nigel Cunningham
2006-01-26  3:45 ` [ 02/23] [Suspend2] Add new include/linux/freezer.h header Nigel Cunningham
2006-01-26  3:45 ` [ 03/23] [Suspend2] Allow a notifier to remove itself from the notifier list Nigel Cunningham
2006-01-26  3:45 ` [ 04/23] [Suspend2] Todo notifier for processes Nigel Cunningham
2006-01-26  3:45 ` [ 05/23] [Suspend2] Make the freezer use todo lists Nigel Cunningham
2006-01-26  3:45 ` [ 06/23] [Suspend2] Disable usermode helper invocations when the freezer is on Nigel Cunningham
2006-01-30 22:05   ` Rafael J. Wysocki
2006-01-31  3:24     ` Nigel Cunningham
2006-01-31 10:58       ` Rafael J. Wysocki
2006-01-31 23:21         ` Nigel Cunningham
2006-02-01  0:33           ` Rafael J. Wysocki
2006-01-26  3:45 ` [ 07/23] [Suspend2] Add which-to-thaw parameter to thaw_processes() calls Nigel Cunningham
2006-01-26  3:45 ` [ 08/23] [Suspend2] New freezer explanation for kernel/power/process.c Nigel Cunningham
2006-01-26  3:45 ` [ 09/23] [Suspend2] Quieten the freezer for normal operation Nigel Cunningham
2006-01-26  3:45 ` [ 10/23] [Suspend2] Add support for freezing filesystem bdevs Nigel Cunningham
2006-01-26  3:45 ` [ 11/23] [Suspend2] Modify freezeable for freezing kernel threads separately Nigel Cunningham
2006-01-26  3:45 ` [ 12/23] [Suspend2] Split freezing of threads according to whether user/kernelspace Nigel Cunningham
2006-01-26  3:45 ` [ 13/23] [Suspend2] Add support for thawing just kernel threads or all threads Nigel Cunningham
2006-01-26  3:45 ` [ 14/23] [Suspend2] Helper for counting freezeable threads of a type Nigel Cunningham
2006-01-26  3:45 ` [ 15/23] [Suspend2] Helper for counting uninterruptible " Nigel Cunningham
2006-01-30 22:18   ` Rafael J. Wysocki
2006-01-30 22:25     ` Pavel Machek
2006-01-31  0:02       ` Rafael J. Wysocki
2006-01-31  9:27         ` [RFC/RFT] finally solve "swsusp fails with mysqld" problem Pavel Machek
2006-01-31 16:17           ` Rafael J. Wysocki
2006-01-31 21:29             ` Pavel Machek
2006-01-31 22:30               ` Rafael J. Wysocki
2006-01-31  5:42       ` Nigel Cunningham [this message]
2006-01-26  3:45 ` [ 16/23] [Suspend2] Helper to signal all threads of a type Nigel Cunningham
2006-01-26  3:46 ` [ 17/23] [Suspend2] Helper to prod processes that should have frozen but haven't Nigel Cunningham
2006-01-26  3:46 ` [ 18/23] [Suspend2] Helper: Did we fail to freeze all threads of a type? Nigel Cunningham
2006-01-26  3:46 ` [ 19/23] [Suspend2] Freeze all threads of a type Nigel Cunningham
2006-01-26  3:46 ` [ 20/23] [Suspend2] Modify process.c includes and export freezer state Nigel Cunningham
2006-01-26  3:46 ` [ 21/23] [Suspend2] Remove unused DEBUG undef Nigel Cunningham
2006-01-26  3:46 ` [ 22/23] [Suspend2] Modify swsusp to thaw kernel threads while eating memory Nigel Cunningham
2006-01-26  3:46 ` [ 23/23] [Suspend2] Don't scan LRU while freezer is on Nigel Cunningham
2006-01-26 11:55 ` [ 00/23] [Suspend2] Freezer Upgrade Patches Pavel Machek
2006-01-26 21:49   ` Nigel Cunningham
2006-01-26 23:10 ` Rafael J. Wysocki
2006-01-27  4:04   ` Nigel Cunningham
2006-01-27 12:18     ` Rafael J. Wysocki
2006-01-27 19:20       ` Nigel Cunningham
2006-01-27 23:22         ` Pavel Machek
2006-01-30  5:54           ` Nigel Cunningham
2006-01-30 11:50             ` Pavel Machek
2006-01-30  7:53       ` Stefan Seyfried
2006-01-30 11:53         ` Rafael J. Wysocki

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