On Tue, Oct 16, 2012 at 03:08:41PM +0800, Ming Lei wrote:
> On Tue, Oct 16, 2012 at 1:49 PM, Minchan Kim <minc...@kernel.org> wrote:
> >
> > Fair enough but it wouldn't be a good idea that add new unlikely branch
> > in allocator's fast path. Please move the check into slow path which could
> > be in __alloc_pages_slowpath.
>
> Thanks for your comment.
>
> I have considered to add the branch into gfp_to_alloc_flags() before,
> but didn't do it because I see that get_page_from_freelist() may use
> the GFP_IO or GFP_FS flag at least in zone_reclaim() path.
Good point. You can check it in __zone_reclaim and change gfp_mask of
scan_control
because it's never hot path.
>
> So could you make sure it is safe to move the branch into
> __alloc_pages_slowpath()? If so, I will add the check into
> gfp_to_alloc_flags().
How about this?
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d976957..b3607fa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2614,10 +2614,16 @@ retry_cpuset:
page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
zonelist, high_zoneidx, alloc_flags,
preferred_zone, migratetype);
- if (unlikely(!page))
+ if (unlikely(!page)) {
+ /*
+ * Resume path can deadlock because block device
+ * isn't active yet.
+ */
+ if (unlikely(tsk_memalloc_no_io(current)))
+ gfp_mask &= ~GFP_IOFS;
page = __alloc_pages_slowpath(gfp_mask, order,
zonelist, high_zoneidx, nodemask,
preferred_zone, migratetype);
+ }
trace_mm_page_alloc(page, order, gfp_mask, migratetype);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b5e45f4..6c2ccdd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3290,6 +3290,16 @@ static int __zone_reclaim(struct zone *zone, gfp_t
gfp_mask, unsigned int order)
};
unsigned long nr_slab_pages0, nr_slab_pages1;
+ if (unlikely(tsk_memalloc_no_io(current))) {
+ sc.gfp_mask &= ~GFP_IOFS;
+ shrink.gfp_mask = sc.gfp_mask;
+ /*
+ * We allow to reclaim only clean pages.
+ * It can affect RECLAIM_SWAP and RECLAIM_WRITE mode
+ * but this is really rare event and allocator can
* fallback to other zones.
+ */
+ sc.may_writepage = 0;
+ sc.may_swap = 0;
+ }
+
cond_resched();
/*
* We need to be able to allocate from the reserves for RECLAIM_SWAP
>
>
> Thanks,
> --
> Ming Lei
>
> --
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--
Kind Regards,
Minchan Kim
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