mm, page_alloc: move cpuset seqcount checking to slowpath

This is a preparation for the following patch to make review simpler.
While the primary motivation is a bug fix, this also simplifies the fast
path, although the moved code is only enabled when cpusets are in use.

Link: http://lkml.kernel.org/r/20170120103843.24587-4-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Ganapatrao Kulkarni <gpkulkarni@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
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 6f28b7e926d165220dcd15cc84f900b2033fc0f3..0df3c089d3af606b3b676f4cf16bde85575de35a 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3523,12 +3523,13 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
        struct page *page = NULL;
        unsigned int alloc_flags;
        unsigned long did_some_progress;
-       enum compact_priority compact_priority = DEF_COMPACT_PRIORITY;
+       enum compact_priority compact_priority;
        enum compact_result compact_result;
-       int compaction_retries = 0;
-       int no_progress_loops = 0;
+       int compaction_retries;
+       int no_progress_loops;
        unsigned long alloc_start = jiffies;
        unsigned int stall_timeout = 10 * HZ;
+       unsigned int cpuset_mems_cookie;
 
        /*
         * In the slowpath, we sanity check order to avoid ever trying to
@@ -3549,6 +3550,12 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
                                (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
                gfp_mask &= ~__GFP_ATOMIC;
 
+retry_cpuset:
+       compaction_retries = 0;
+       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
@@ -3720,6 +3727,15 @@ retry:
        }
 
 nopage:
+       /*
+        * When updating a task's mems_allowed, it is possible to race with
+        * parallel threads in such a way that an allocation can fail while
+        * the mask is being updated. If a page allocation is about to fail,
+        * check if the cpuset changed during allocation and if so, retry.
+        */
+       if (read_mems_allowed_retry(cpuset_mems_cookie))
+               goto retry_cpuset;
+
        warn_alloc(gfp_mask,
                        "page allocation failure: order:%u", order);
 got_pg:
@@ -3734,7 +3750,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
                        struct zonelist *zonelist, nodemask_t *nodemask)
 {
        struct page *page;
-       unsigned int cpuset_mems_cookie;
        unsigned int alloc_flags = ALLOC_WMARK_LOW;
        gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
        struct alloc_context ac = {
@@ -3771,9 +3786,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
        if (IS_ENABLED(CONFIG_CMA) && ac.migratetype == MIGRATE_MOVABLE)
                alloc_flags |= ALLOC_CMA;
 
-retry_cpuset:
-       cpuset_mems_cookie = read_mems_allowed_begin();
-
        /* Dirty zone balancing only done in the fast path */
        ac.spread_dirty_pages = (gfp_mask & __GFP_WRITE);
 
@@ -3786,6 +3798,11 @@ retry_cpuset:
                                        ac.high_zoneidx, ac.nodemask);
        if (!ac.preferred_zoneref->zone) {
                page = NULL;
+               /*
+                * This might be due to race with cpuset_current_mems_allowed
+                * update, so make sure we retry with original nodemask in the
+                * slow path.
+                */
                goto no_zone;
        }
 
@@ -3794,6 +3811,7 @@ retry_cpuset:
        if (likely(page))
                goto out;
 
+no_zone:
        /*
         * Runtime PM, block IO and its error handling path can deadlock
         * because I/O on the device might not complete.
@@ -3811,24 +3829,11 @@ retry_cpuset:
                ac.nodemask = nodemask;
                ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
                                                ac.high_zoneidx, ac.nodemask);
-               if (!ac.preferred_zoneref->zone)
-                       goto no_zone;
+               /* If we have NULL preferred zone, slowpath wll handle that */
        }
 
        page = __alloc_pages_slowpath(alloc_mask, order, &ac);
 
-no_zone:
-       /*
-        * When updating a task's mems_allowed, it is possible to race with
-        * parallel threads in such a way that an allocation can fail while
-        * the mask is being updated. If a page allocation is about to fail,
-        * check if the cpuset changed during allocation and if so, retry.
-        */
-       if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie))) {
-               alloc_mask = gfp_mask;
-               goto retry_cpuset;
-       }
-
 out:
        if (memcg_kmem_enabled() && (gfp_mask & __GFP_ACCOUNT) && page &&
            unlikely(memcg_kmem_charge(page, gfp_mask, order) != 0)) {