Messages in this thread | | | Subject | Re: [PATCH 07/12] mm, page_alloc: Distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd | From | Vlastimil Babka <> | Date | Wed, 26 Aug 2015 18:24:34 +0200 |
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On 08/26/2015 04:45 PM, Mel Gorman wrote: > On Tue, Aug 25, 2015 at 05:37:59PM +0200, Vlastimil Babka wrote: >>> @@ -2158,7 +2158,7 @@ static bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order) >>> return false; >>> if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM)) >>> return false; >>> - if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & __GFP_WAIT)) >>> + if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM))) >>> return false; >>> >>> return should_fail(&fail_page_alloc.attr, 1 << order); >> >> IIUC ignore_gfp_wait tells it to assume that reclaimers will eventually >> succeed (for some reason?), so they shouldn't fail. Probably to focus the >> testing on atomic allocations. But your change makes atomic allocation never >> fail, so that goes against the knob IMHO? >> > > Fair point, I'll remove the __GFP_ATOMIC check. I felt this was a sensible > but then again deliberately failing allocations makes my brain twitch a > bit. In retrospect, someone who cared should add a ignore_gfp_atomic knob.
Thanks.
>>> @@ -2660,7 +2660,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...) >>> if (test_thread_flag(TIF_MEMDIE) || >>> (current->flags & (PF_MEMALLOC | PF_EXITING))) >>> filter &= ~SHOW_MEM_FILTER_NODES; >>> - if (in_interrupt() || !(gfp_mask & __GFP_WAIT)) >>> + if (in_interrupt() || !(gfp_mask & __GFP_WAIT) || (gfp_mask & __GFP_ATOMIC)) >>> filter &= ~SHOW_MEM_FILTER_NODES; >>> >>> if (fmt) { >> >> This caught me previously and I convinced myself that it's OK, but now I'm >> not anymore. IIUC this is to not filter nodes by mems_allowed during >> printing, if the allocation itself wasn't limited? In that case it should >> probably only look at __GFP_ATOMIC after this patch? As that's the only >> thing that determines ALLOC_CPUSET. >> I don't know where in_interrupt() comes from, but it was probably considered >> in the past, as can be seen in zlc_setup()? >> > > I assumed the in_interrupt() thing was simply because cpusets were the > primary means of limiting allocations of interest to the author at the > time.
IIUC this hunk is unrelated to the previous one - not about limiting allocations, but printing allocation warnings. Which includes the state of nodes where the allocation was allowed to try. And ~SHOW_MEM_FILTER_NODES means it was allowed everywhere, so the printing won't filter by mems_allowed.
> I guess now that I think about it more that a more sensible check would > be against __GFP_DIRECT_RECLAIM because that covers the interesting > cases.
I think the most robust check would be to rely on what was already prepared by gfp_to_alloc_flags(), instead of repeating it here. So add alloc_flags parameter to warn_alloc_failed(), and drop the filter when - ALLOC_CPUSET is not set, as that disables the cpuset checks - ALLOC_NO_WATERMARKS is set, as that allows calling __alloc_pages_high_priority() attempt which ignores cpusets
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