Messages in this thread | | | Date | Tue, 25 Oct 2011 18:46:10 -0700 | Subject | Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations | From | Colin Cross <> |
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On Tue, Oct 25, 2011 at 3:18 PM, David Rientjes <rientjes@google.com> wrote: > On Tue, 25 Oct 2011, Mel Gorman wrote: > >> That said, it will be difficult to remember why checking __GFP_NOFAIL in >> this case is necessary and someone might "optimitise" it away later. It >> would be preferable if it was self-documenting. Maybe something like >> this? (This is totally untested) >> > > __GFP_NOFAIL _should_ be optimized away in this case because all he's > passing is __GFP_WAIT | __GFP_NOFAIL. That doesn't make any sense unless > all you want to do is livelock.
__GFP_NOFAIL is not set in the case that I care about. If my change is hit, no forward progress has been made, so I agree it should not honor __GFP_NOFAIL.
> __GFP_NOFAIL doesn't mean the page allocator would infinitely loop in all > conditions. That's why GFP_ATOMIC | __GFP_NOFAIL actually fails, and I > would argue that __GFP_WAIT | __GFP_NOFAIL should fail as well since it's > the exact same condition except doesn't have access to the extra memory > reserves. > > Suspend needs to either set __GFP_NORETRY to avoid the livelock if it's > going to disable all means of memory reclaiming or freeing in the page > allocator. Or, better yet, just make it GFP_NOWAIT. >
It would be nice to give compaction and the slab shrinker a chance to recover a few pages, both methods will work fine in suspend. GFP_NOWAIT will prevent them from ever running, and __GFP_NORETRY will give up even if they are making progress but haven't recovered enough pages.
Converting suspend to GFP_NOWAIT would simply be ~GFP_KERNEL instead of ~GFP_IOFS in pm_restrict_gfp_mask(). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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