On Mon, 23 Jan 2017 13:16:12 +0100 Arnd Bergmann <arnd@xxxxxxxx> wrote: > The __alloc_pages_slowpath() has gotten rather complex and gcc > is no longer able to follow the gotos and prove that the > alloc_flags variable is initialized at the time it is used: > > mm/page_alloc.c: In function '__alloc_pages_slowpath': > mm/page_alloc.c:3565:15: error: 'alloc_flags' may be used uninitialized in this function [-Werror=maybe-uninitialized] > > To be honest, I can't figure that out either, maybe it is or > maybe not, but moving the existing initialization up a little > higher looks safe and makes it obvious to both me and gcc that > the initialization comes before the first use. > > ... > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3591,6 +3591,13 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM))) > gfp_mask &= ~__GFP_ATOMIC; > > + /* > + * The fast path uses conservative alloc_flags to succeed only until > + * kswapd needs to be woken up, and to avoid the cost of setting up > + * alloc_flags precisely. So we do that now. > + */ > + alloc_flags = gfp_to_alloc_flags(gfp_mask); > + > retry_cpuset: > compaction_retries = 0; > no_progress_loops = 0; > @@ -3607,14 +3614,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > if (!ac->preferred_zoneref->zone) > goto nopage; > > - > - /* > - * The fast path uses conservative alloc_flags to succeed only until > - * kswapd needs to be woken up, and to avoid the cost of setting up > - * alloc_flags precisely. So we do that now. > - */ > - alloc_flags = gfp_to_alloc_flags(gfp_mask); > - > if (gfp_mask & __GFP_KSWAPD_RECLAIM) > wake_all_kswapds(order, ac); hm. But we later do if (gfp_pfmemalloc_allowed(gfp_mask)) alloc_flags = ALLOC_NO_WATERMARKS; ... if (read_mems_allowed_retry(cpuset_mems_cookie)) goto retry_cpuset; so with your patch there's a path where we can rerun everything with alloc_flags == ALLOC_NO_WATERMARKS. That's changed behaviour. When I saw the test robot warning I did this, which I think preserves behaviour? --- a/mm/page_alloc.c~mm-consolidate-gfp_nofail-checks-in-the-allocator-slowpath-fix +++ a/mm/page_alloc.c @@ -3577,6 +3577,14 @@ retry_cpuset: no_progress_loops = 0; compact_priority = DEF_COMPACT_PRIORITY; cpuset_mems_cookie = read_mems_allowed_begin(); + + /* + * The fast path uses conservative alloc_flags to succeed only until + * kswapd needs to be woken up, and to avoid the cost of setting up + * alloc_flags precisely. So we do that now. + */ + alloc_flags = gfp_to_alloc_flags(gfp_mask); + /* * We need to recalculate the starting point for the zonelist iterator * because we might have used different nodemask in the fast path, or @@ -3588,14 +3596,6 @@ retry_cpuset: if (!ac->preferred_zoneref->zone) goto nopage; - - /* - * The fast path uses conservative alloc_flags to succeed only until - * kswapd needs to be woken up, and to avoid the cost of setting up - * alloc_flags precisely. So we do that now. - */ - alloc_flags = gfp_to_alloc_flags(gfp_mask); - if (gfp_mask & __GFP_KSWAPD_RECLAIM) wake_all_kswapds(order, ac); _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
