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    SubjectRe: VM/VFS bug with large amount of memory and file systems?
    On Mon, 17 Sep 2007 13:11:14 -0400
    Rik van Riel <> wrote:

    > > I'm guessing there is no pressure at all on zone_highmem so the
    > > kernel will not try to reclaim pagecache. And because the pagecache
    > > pages are happily sitting there, the buggerheads are pinned and do not
    > > get reclaimed.

    yeah, this got pretty unavoidably broken when we killed the global LRU
    in 2.5.early. It's odd that it took this long for someone to hit it.

    > I've got code for this in RHEL 3, but never bothered to
    > merge it upstream since I thought people with large memory
    > systems would be running 64 bit kernels by now.
    > Obviously I was wrong. Andrew, are you interested in a
    > fix for this problem?
    > IIRC I simply kept a list of all buffer heads and walked
    > that to reclaim pages when the number of buffer heads is
    > too high (and we need memory). This list can be maintained
    > in places where we already hold the lock for the buffer head
    > freelist, so there should be no additional locking overhead
    > (again, IIRC).

    Christoph's slab defragmentation code should permit us to fix this:
    grab a page of buffer_heads off the slab lists, trylock the page,
    strip the buffer_heads. I think that would be a better approach
    if we can get it going because it's more general.
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      Last update: 2007-09-17 22:19    [W:0.040 / U:0.712 seconds]
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