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    SubjectRe: Memory Problem in 2.4.9 ?
    Date
    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.)

    > 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]?

    > > 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?

    --
    Daniel
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