mm, page_alloc: set alloc_flags only once in slowpath

In __alloc_pages_slowpath(), alloc_flags doesn't change after it's
initialized, so move the initialization above the retry: label.  Also
make the comment above the initialization more descriptive.

The only exception in the alloc_flags being constant is
ALLOC_NO_WATERMARKS, which may change due to TIF_MEMDIE being set on the
allocating thread.  We can fix this, and make the code simpler and a bit
more effective at the same time, by moving the part that determines
ALLOC_NO_WATERMARKS from gfp_to_alloc_flags() to gfp_pfmemalloc_allowed().

This means we don't have to mask out ALLOC_NO_WATERMARKS in numerous
places in __alloc_pages_slowpath() anymore.  The only two tests for the
flag can instead call gfp_pfmemalloc_allowed().

Link: http://lkml.kernel.org/r/20160721073614.24395-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c281125..5703f7f 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3119,8 +3119,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
         */
        count_vm_event(COMPACTSTALL);
 
-       page = get_page_from_freelist(gfp_mask, order,
-                                       alloc_flags & ~ALLOC_NO_WATERMARKS, ac);
+       page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
 
        if (page) {
                struct zone *zone = page_zone(page);
@@ -3288,8 +3287,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
                return NULL;
 
 retry:
-       page = get_page_from_freelist(gfp_mask, order,
-                                       alloc_flags & ~ALLOC_NO_WATERMARKS, ac);
+       page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
 
        /*
         * If an allocation failed after direct reclaim, it could be because
@@ -3351,16 +3349,6 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
        } else if (unlikely(rt_task(current)) && !in_interrupt())
                alloc_flags |= ALLOC_HARDER;
 
-       if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
-               if (gfp_mask & __GFP_MEMALLOC)
-                       alloc_flags |= ALLOC_NO_WATERMARKS;
-               else if (in_serving_softirq() && (current->flags & PF_MEMALLOC))
-                       alloc_flags |= ALLOC_NO_WATERMARKS;
-               else if (!in_interrupt() &&
-                               ((current->flags & PF_MEMALLOC) ||
-                                unlikely(test_thread_flag(TIF_MEMDIE))))
-                       alloc_flags |= ALLOC_NO_WATERMARKS;
-       }
 #ifdef CONFIG_CMA
        if (gfpflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
                alloc_flags |= ALLOC_CMA;
@@ -3370,7 +3358,19 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 
 bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
 {
-       return !!(gfp_to_alloc_flags(gfp_mask) & ALLOC_NO_WATERMARKS);
+       if (unlikely(gfp_mask & __GFP_NOMEMALLOC))
+               return false;
+
+       if (gfp_mask & __GFP_MEMALLOC)
+               return true;
+       if (in_serving_softirq() && (current->flags & PF_MEMALLOC))
+               return true;
+       if (!in_interrupt() &&
+                       ((current->flags & PF_MEMALLOC) ||
+                        unlikely(test_thread_flag(TIF_MEMDIE))))
+               return true;
+
+       return false;
 }
 
 static inline bool is_thp_gfp_mask(gfp_t gfp_mask)
@@ -3503,36 +3503,36 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
                                (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
                gfp_mask &= ~__GFP_ATOMIC;
 
-retry:
-       if (gfp_mask & __GFP_KSWAPD_RECLAIM)
-               wake_all_kswapds(order, ac);
-
        /*
-        * OK, we're below the kswapd watermark and have kicked background
-        * reclaim. Now things get more complex, so set up alloc_flags according
-        * to how we want to proceed.
+        * 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:
+       if (gfp_mask & __GFP_KSWAPD_RECLAIM)
+               wake_all_kswapds(order, ac);
+
        /*
         * Reset the zonelist iterators if memory policies can be ignored.
         * These allocations are high priority and system rather than user
         * orientated.
         */
-       if ((alloc_flags & ALLOC_NO_WATERMARKS) || !(alloc_flags & ALLOC_CPUSET)) {
+       if (!(alloc_flags & ALLOC_CPUSET) || gfp_pfmemalloc_allowed(gfp_mask)) {
                ac->zonelist = node_zonelist(numa_node_id(), gfp_mask);
                ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
                                        ac->high_zoneidx, ac->nodemask);
        }
 
        /* This is the last chance, in general, before the goto nopage. */
-       page = get_page_from_freelist(gfp_mask, order,
-                               alloc_flags & ~ALLOC_NO_WATERMARKS, ac);
+       page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
        if (page)
                goto got_pg;
 
        /* Allocate without watermarks if the context allows */
-       if (alloc_flags & ALLOC_NO_WATERMARKS) {
+       if (gfp_pfmemalloc_allowed(gfp_mask)) {
+
                page = get_page_from_freelist(gfp_mask, order,
                                                ALLOC_NO_WATERMARKS, ac);
                if (page)