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    SubjectRe: Strange dcache memory pressure when highmem enabled
    On Tue, Oct 14, 2003 at 10:43:52PM -0700, Andrew Morton wrote:
    > Neil Brown <neilb@cse.unsw.edu.au> wrote:
    > >
    > > I noticed that shrink_caches calls shrink_dcache_memory independant
    > > of the classzone that is being shrunk. So if we are trying to
    > > shrink ZONE_HIGHMEM, the dentry_cache is shrunk, even though the
    > > dentry_cache doesn't live in highmem. However I'm not sure if I have
    > > understood the classzones well enough for that observation even to
    > > make sense.
    >
    > Makes heaps of sense. Here's an instabackport of what we did in 2.6:
    >
    > mm/vmscan.c | 12 +++++++++---
    > 1 files changed, 9 insertions(+), 3 deletions(-)
    >
    > diff -puN mm/vmscan.c~a mm/vmscan.c
    > --- 24/mm/vmscan.c~a 2003-10-14 22:41:34.000000000 -0700
    > +++ 24-akpm/mm/vmscan.c 2003-10-14 22:42:22.000000000 -0700
    > @@ -640,11 +640,17 @@ int try_to_free_pages_zone(zone_t *class
    > nr_pages = shrink_caches(classzone, gfp_mask, nr_pages, &failed_swapout);
    > if (nr_pages <= 0)
    > return 1;
    > - shrink_dcache_memory(vm_vfs_scan_ratio, gfp_mask);
    > - shrink_icache_memory(vm_vfs_scan_ratio, gfp_mask);
    > + if (classzone - classzone->zone_pgdat->node_zones <
    > + ZONE_HIGHMEM) {
    > + shrink_dcache_memory(vm_vfs_scan_ratio,
    > + gfp_mask);
    > + shrink_icache_memory(vm_vfs_scan_ratio,
    > + gfp_mask);
    > #ifdef CONFIG_QUOTA
    > - shrink_dqcache_memory(vm_vfs_scan_ratio, gfp_mask);
    > + shrink_dqcache_memory(vm_vfs_scan_ratio,
    > + gfp_mask);
    > #endif
    > + }
    > if (!failed_swapout)
    > failed_swapout = !swap_out(classzone);
    > } while (--tries);

    An highmem user can make use of lowmem too. Think a 1G box, it looks
    wrong to disallow highmem to shrink the 800M of dcache in the normal/dma
    zones.

    I wonder if what he's suffering from is a reduced normal zone due the
    mem_map_t being larger. The reduced normal zone will trigger the dcache
    shrinking more frequently. But he may want to try again with 2.4.23pre7
    with a classzone aware refill_inactive that will ensure the inactive
    list has enough lowmem pages before shrink_caches claims failure.

    Andrea - If you prefer relying on open source software, check these links:
    rsync.kernel.org::pub/scm/linux/kernel/bkcvs/linux-2.[45]/
    http://www.cobite.com/cvsps/
    -
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