Messages in this thread |  | | | From | "Rafael J. Wysocki" <> | | Subject | Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it | | Date | Tue, 3 Nov 2009 22:51:53 +0100 |
On Tuesday 03 November 2009, KOSAKI Motohiro wrote: > > On Monday 02 November 2009, KOSAKI Motohiro wrote: > > > > > Then, This patch changed shrink_all_memory() to only the wrapper function of > > > > > do_try_to_free_pages(). it bring good reviewability and debuggability, and solve > > > > > above problems. > > > > > > > > > > side note: Reclaim logic unificication makes two good side effect. > > > > > - Fix recursive reclaim bug on shrink_all_memory(). > > > > > it did forgot to use PF_MEMALLOC. it mean the system be able to stuck into deadlock. > > > > > - Now, shrink_all_memory() got lockdep awareness. it bring good debuggability. > > > > > > > > As I said previously, I don't really see a reason to keep shrink_all_memory(). > > > > > > > > Do you think that removing it will result in performance degradation? > > > > > > Hmm... > > > Probably, I misunderstood your mention. I thought you suggested to kill > > > all hibernation specific reclaim code. I did. It's no performance degression. > > > (At least, I didn't observe) > > > > > > But, if you hope to kill shrink_all_memory() function itsef, the short answer is, > > > it's impossible. > > > > > > Current VM reclaim code need some preparetion to caller, and there are existing in > > > both alloc_pages_slowpath() and try_to_free_pages(). We can't omit its preparation. > > > > Well, my grepping for 'shrink_all_memory' throughout the entire kernel source > > code seems to indicate that hibernate_preallocate_memory() is the only current > > user of it. I may be wrong, but I doubt it, unless some new users have been > > added since 2.6.31. > > > > In case I'm not wrong, it should be safe to drop it from > > hibernate_preallocate_memory(), because it's there for performance reasons > > only. Now, since hibernate_preallocate_memory() appears to be the only user of > > it, it should be safe to drop it entirely. > > Hmmm... > I've try the dropping shrink_all_memory() today. but I've got bad result. > > In 3 times test, result were > > 2 times: kernel hang-up ;) > 1 time: success, but make slower than with shrink_all_memory() about 100x times. > > > Did you try to drop it yourself on your machine? Is this success?
Generally, yes, but the performance was hit really badly.
So, the conclusion is that we need shrink_all_memory() for things to work, which is kind of interesting.
In that case, please feel free to add Acked-by: Rafael J. Wysocki <rjw@sisk.pl> to the patch.
Thanks, Rafael
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