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    SubjectRe: [patch -mm 8/9 v2] oom: avoid oom killer for lowmem allocations
    On Mon, 15 Feb 2010 14:20:21 -0800 (PST)
    David Rientjes <rientjes@google.com> wrote:

    > If memory has been depleted in lowmem zones even with the protection
    > afforded to it by /proc/sys/vm/lowmem_reserve_ratio, it is unlikely that
    > killing current users will help. The memory is either reclaimable (or
    > migratable) already, in which case we should not invoke the oom killer at
    > all, or it is pinned by an application for I/O. Killing such an
    > application may leave the hardware in an unspecified state and there is
    > no guarantee that it will be able to make a timely exit.
    >
    > Lowmem allocations are now failed in oom conditions so that the task can
    > perhaps recover or try again later. Killing current is an unnecessary
    > result for simply making a GFP_DMA or GFP_DMA32 page allocation and no
    > lowmem allocations use the now-deprecated __GFP_NOFAIL bit so retrying is
    > unnecessary.
    >
    > Previously, the heuristic provided some protection for those tasks with
    > CAP_SYS_RAWIO, but this is no longer necessary since we will not be
    > killing tasks for the purposes of ISA allocations.
    >
    > high_zoneidx is gfp_zone(gfp_flags), meaning that ZONE_NORMAL will be the
    > default for all allocations that are not __GFP_DMA, __GFP_DMA32,
    > __GFP_HIGHMEM, and __GFP_MOVABLE on kernels configured to support those
    > flags. Testing for high_zoneidx being less than ZONE_NORMAL will only
    > return true for allocations that have either __GFP_DMA or __GFP_DMA32.
    >
    > Acked-by: Rik van Riel <riel@redhat.com>
    > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > Signed-off-by: David Rientjes <rientjes@google.com>
    > ---
    > mm/page_alloc.c | 3 +++
    > 1 files changed, 3 insertions(+), 0 deletions(-)
    >
    > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -1914,6 +1914,9 @@ rebalance:
    > * running out of options and have to consider going OOM
    > */
    > if (!did_some_progress) {
    > + /* The oom killer won't necessarily free lowmem */
    > + if (high_zoneidx < ZONE_NORMAL)
    > + goto nopage;
    > if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
    > if (oom_killer_disabled)
    > goto nopage;

    WARN_ON((high_zoneidx < ZONE_NORMAL) && (gfp_mask & __GFP_NOFAIL))
    plz.

    Thanks,
    -Kame



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