Messages in this thread | | | Date | Wed, 22 Aug 2001 22:19:19 -0300 (BRT) | From | Marcelo Tosatti <> | Subject | Re: Memory Problem in 2.4.9 ? |
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On Thu, 23 Aug 2001, Daniel Phillips wrote:
> On August 23, 2001 02:10 am, Marcelo Tosatti wrote: > > On Thu, 23 Aug 2001, Daniel Phillips wrote: > > > > > On August 22, 2001 09:05 pm, Marcelo Tosatti wrote: > > > > On Wed, 22 Aug 2001, Daniel Phillips wrote: > > > > > What can we do right now? We could always just comment out the alloc failed > > > > > message. The result will be a lot of busy waiting on dirty page writeout > > > > > which will work but it will keep us from focussing on the question: how did > > > > > we get so short of bounce buffers? Well, maybe we are submitting too much IO > > > > > without intelligent throttling (/me waves at Ben). That sounds like the > > > > > place to attack first. > > > > > > > > We can just wait on the writeout of lowmem buffers at page_launder() > > > > (which will not cause IO buffering since we are doing lowmem IO, duh), and > > > > then we are done. > > > > > > > > Take a look at the patch I posted before (__GFP_NOBOUNCE). > > > > > > A little light reading for a Wednesday afternoon ;-) > > > > > > Nice hack, way to go. So this will wait synchronously in try_to_free_buffers > > > if we have to go around twice in alloc_bounce_page or alloc_bounce_bh (the > > > latter eventually resulting in a page_alloc from kmem_cache grow). > > > > Not synchronously, no. It will just allow allocations trying to get memory > > for bounce buffering to block on lowmem IO. > > Whoops, it's been a while since I read page_launder. Hey! Major cleanup. > It's much easier to understand what it's doing now. > > OK, sync_page_buffers no longer does what its name says, or implements what > its comment says it does. Now the GFP_WAIT just means wait on already-locked > buffers so that IO can be initiated. (By the way, there are bunch of > comments in try_to_free_buffers that lie now.) OK, so the busy wait is > implemented in alloc_bounce_page, and page_launder is just used to start IO, > fine. Hmm, I think I will try my semaphore idea, not because you haven't > solved the problem, but because I think a lot of CPU-wasting trips into > page_launder could be eliminated. (A 2.5 thing of course.)
There is no real CPU-wasting trips into page_launder().
As soon as we find a dirty, lowmem, unlocked page with ->buffers, we block on IO there.
> > With this behaviour, its safe to completly remove Ingo's emergency scheme. > > Yes, so why don't you add that to your patch, and also the correction to the > page->zone test and call it [PATCH]?
Will do it soon. > > > > What does SLAB_LEVEL_MASK do? Did you find out by hitting the BUG when you > > > tried the patch? Anyway, it needs a comment. > > > > SLAB_LEVEL_MASK is the mask for SLAB-valid allocations. > > And "LEVEL" means?
No idea. Nothing, probably.
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