mm/vmscan.c: condense scan_control (bb451fdf) · Commits · 戴 / test

Use smaller scan_control fields for order, priority, and reclaim_idx. Convert fields from int => s8. All easily fit within a byte: - allocation order range: 0..MAX_ORDER(64?) - priority range: 0..12(DEF_PRIORITY) - reclaim_idx range: 0..6(__MAX_NR_ZONES) Since ("x86_64: expand kernel stack to 16K") x86_64 stack overflows are not an issue. But it's inefficient to use ints. Use s8 (signed byte) rather than u8 to allow for loops like: do { ... } while (--sc.priority >= 0); Add BUILD_BUG_ON to verify that s8 is capable of storing max values. This reduces sizeof(struct scan_control): - 96 => 80 bytes (x86_64) - 68 => 56 bytes (i386) scan_control structure field order is changed to utilize padding. After this patch there is 1 bit of scan_control padding. akpm: makes my vmscan.o's .text 572 bytes smaller as well. Link: http://lkml.kernel.org/r/20180530061212.84915-1-gthelen@google.com Signed-off-by:

Greg Thelen <gthelen@google.com> Suggested-by:

Matthew Wilcox <willy@infradead.org> Reviewed-by:

Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+20 −12

Original line number	Diff line number	Diff line
		@@ -65,12 +65,6 @@ struct scan_control {
		/* How many pages shrink_list() should reclaim */
		unsigned long nr_to_reclaim;

		/* This context's GFP mask */
		gfp_t gfp_mask;

		/* Allocation order */
		int order;

		/*
		* Nodemask of nodes allowed by the caller. If NULL, all nodes
		* are scanned.
		@@ -83,12 +77,6 @@ struct scan_control {
		*/
		struct mem_cgroup *target_mem_cgroup;

		/* Scan (total_size >> priority) pages at once */
		int priority;

		/* The highest zone to isolate pages for reclaim from */
		enum zone_type reclaim_idx;

		/* Writepage batching in laptop mode; RECLAIM_WRITE */
		unsigned int may_writepage:1;

		@@ -111,6 +99,18 @@ struct scan_control {
		/* One of the zones is ready for compaction */
		unsigned int compaction_ready:1;

		/* Allocation order */
		s8 order;

		/* Scan (total_size >> priority) pages at once */
		s8 priority;

		/* The highest zone to isolate pages for reclaim from */
		s8 reclaim_idx;

		/* This context's GFP mask */
		gfp_t gfp_mask;

		/* Incremented by the number of inactive pages that were scanned */
		unsigned long nr_scanned;

		@@ -3063,6 +3063,14 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
		.may_swap = 1,
		};

		/*
		* scan_control uses s8 fields for order, priority, and reclaim_idx.
		* Confirm they are large enough for max values.
		*/
		BUILD_BUG_ON(MAX_ORDER > S8_MAX);
		BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
		BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);

		/*
		* Do not enter reclaim if fatal signal was delivered while throttled.
		* 1 is returned so that the page allocator does not OOM kill at this

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