On Mon, 15 Feb 2010 16:10:15 -0800 (PST)
David Rientjes <rientjes@xxxxxxxxxx> wrote:
> On Tue, 16 Feb 2010, KAMEZAWA Hiroyuki 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.
> >
>
> As I already explained when you first brought this up, the possibility of
> not invoking the oom killer is not unique to GFP_DMA, it is also possible
> for GFP_NOFS. Since __GFP_NOFAIL is deprecated and there are no current
> users of GFP_DMA | __GFP_NOFAIL, that warning is completely unnecessary.
> We're not adding any additional __GFP_NOFAIL allocations.
>
Please add documentation about that to gfp.h before doing this.
Doing this without writing any documenation is laziness.
(WARNING is a style of documentation.)
Thanks,
-Kame
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