Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] Thaw userspace and kernel space separately. | Date | Mon, 23 Oct 2006 20:37:13 +0200 |
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On Monday, 23 October 2006 18:51, Andrew Morton wrote: > > On Mon, 23 Oct 2006 22:00:11 +1000 Nigel Cunningham <ncunningham@linuxmail.org> wrote: > > Hi. > > > > On Mon, 2006-10-23 at 12:26 +0200, Rafael J. Wysocki wrote: > > > On Monday, 23 October 2006 01:48, Nigel Cunningham wrote: > > > > Modify process thawing so that we can thaw kernel space without thawing > > > > userspace, and thaw kernelspace first. This will be useful in later > > > > patches, where I intend to get swsusp thawing kernel threads only before > > > > seeking to free memory. > > > > > > Please explain why you think it will be necessary/useful. > > > > > > I remember a discussion about it some time ago that didn't indicate > > > we would need/want to do this. > > > > This is needed to make suspending faster and more reliable when the > > system is in a low memory situation. Imagine that you have a number of > > processes trying to allocate memory at the time you're trying to > > suspend. They want so much memory that when you come to prepare the > > image, you find that you need to free pages. But your swapfile is on > > ext3, and you've just frozen all processes, so any attempt to free > > memory could result in a deadlock while the vm tries to swap out pages > > using the frozen kjournald. So you need to thaw processes to free the > > memory. But thawing processes will start the processes allocating memory > > again, so you'll be fighting an uphill battle. > > > > If you can only thaw the kernel threads, you can free memory without > > restarting userspace or deadlocking against a frozen kjournald. > > > > kjournald will not participate in writing to swapfiles. > > The situation where we would need this feature is where the loop driver is > involved in the path-to-disk. But I doubt if that's a thing we'd want to > support. > > otoh there may be other kernel threads which are a saner thing to have in > the swapout path and which we do want to support. md_thread, perhaps?
md_thread needs some consideration I think. Having a swapfile on RAID is a legit thing and we should support that.
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