On Mon, 15 Feb 2010 14:20:21 -0800 (PST)
David Rientjes <rientjes@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> 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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