> oom: avoid oom killer for lowmem allocations
I think the terminology is poor. My 256MB test box only has lowmem!
In the past we've used the term "lower zone" here, which is I think
what you want?
On Sun, 6 Jun 2010 15:34:38 -0700 (PDT)
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.
Killing an application can leave hardware in an unspecified state? How
so? That means a ^C kills the box!
> Lowmem allocations are now failed in oom conditions when __GFP_NOFAIL is
> not used so that the task can perhaps recover or try again later.
>
> 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: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 29 ++++++++++++++++++++---------
> 1 files changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1759,6 +1759,9 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> /* The OOM killer will not help higher order allocs */
> if (order > PAGE_ALLOC_COSTLY_ORDER)
> goto out;
> + /* The OOM killer does not needlessly kill tasks for lowmem */
a) terminology is scary
b) comment doesn't explain _why_, which is the most important thing
to explain.
> + if (high_zoneidx < ZONE_NORMAL)
> + goto out;
> /*
> * GFP_THISNODE contains __GFP_NORETRY and we never hit this.
> * Sanity check for bare calls of __GFP_THISNODE, not real OOM.
> @@ -2052,15 +2055,23 @@ rebalance:
> if (page)
> goto got_pg;
>
> - /*
> - * The OOM killer does not trigger for high-order
> - * ~__GFP_NOFAIL allocations so if no progress is being
> - * made, there are no other options and retrying is
> - * unlikely to help.
> - */
> - if (order > PAGE_ALLOC_COSTLY_ORDER &&
> - !(gfp_mask & __GFP_NOFAIL))
> - goto nopage;
> + if (!(gfp_mask & __GFP_NOFAIL)) {
> + /*
> + * The oom killer is not called for high-order
> + * allocations that may fail, so if no progress
> + * is being made, there are no other options and
> + * retrying is unlikely to help.
> + */
> + if (order > PAGE_ALLOC_COSTLY_ORDER)
> + goto nopage;
> + /*
> + * The oom killer is not called for lowmem
> + * allocations to prevent needlessly killing
> + * innocent tasks.
> + */
s/lowmem/somethingelse/
> + if (high_zoneidx < ZONE_NORMAL)
> + goto nopage;
> + }
>
> goto restart;
> }
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