mm: apply per-task gfp constraints in fast path

Function current_gfp_context() is called after fast path.  However, soon
we will add more constraints which will also limit zones based on
context.  Move this call into fast path, and apply the correct
constraints for all allocations.

Also update .reclaim_idx based on value returned by
current_gfp_context() because it soon will modify the allowed zones.

Note:
With this patch we will do one extra current->flags load during fast path,
but we already load current->flags in fast-path:

__alloc_pages()
 prepare_alloc_pages()
  current_alloc_flags(gfp_mask, *alloc_flags);

Later, when we add the zone constrain logic to current_gfp_context() we
will be able to remove current->flags load from current_alloc_flags, and
therefore return fast-path to the current performance level.

Link: https://lkml.kernel.org/r/20210215161349.246722-7-pasha.tatashin@soleen.comSigned-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Suggested-by: Michal Hocko <mhocko@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -5180,6 +5180,13 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
 	}
 
 	gfp &= gfp_allowed_mask;
+	/*
+	 * Apply scoped allocation constraints. This is mainly about GFP_NOFS
+	 * resp. GFP_NOIO which has to be inherited for all allocation requests
+	 * from a particular context which has been marked by
+	 * memalloc_no{fs,io}_{save,restore}.
+	 */
+	gfp = current_gfp_context(gfp);
 	alloc_gfp = gfp;
 	if (!prepare_alloc_pages(gfp, order, preferred_nid, nodemask, &ac,
 			&alloc_gfp, &alloc_flags))
@@ -5196,13 +5203,7 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
 	if (likely(page))
 		goto out;
 
-	/*
-	 * Apply scoped allocation constraints. This is mainly about GFP_NOFS
-	 * resp. GFP_NOIO which has to be inherited for all allocation requests
-	 * from a particular context which has been marked by
-	 * memalloc_no{fs,io}_{save,restore}.
-	 */
-	alloc_gfp = current_gfp_context(gfp);
+	alloc_gfp = gfp;
 	ac.spread_dirty_pages = false;
 
 	/*