[V3] mm, compaction: don't use ALLOC_CMA in long term GUP flow

Commit Message

Ge Yang Dec. 15, 2024, 7:49 a.m. UTC

From: yangge <[e-mail]>

Since commit 984fdba6a32e ("mm, compaction: use proper alloc_flags
in __compaction_suitable()") allow compaction to proceed when free
pages required for compaction reside in the CMA pageblocks, it's
possible that __compaction_suitable() always returns true, and in
some cases, it's not acceptable.

There are 4 NUMA nodes on my machine, and each NUMA node has 32GB
of memory. I have configured 16GB of CMA memory on each NUMA node,
and starting a 32GB virtual machine with device passthrough is
extremely slow, taking almost an hour.

During the start-up of the virtual machine, it will call
pin_user_pages_remote(..., FOLL_LONGTERM, ...) to allocate memory.
Long term GUP cannot allocate memory from CMA area, so a maximum
of 16 GB of no-CMA memory on a NUMA node can be used as virtual
machine memory. Since there is 16G of free CMA memory on the NUMA
node, watermark for order-0 always be met for compaction, so
__compaction_suitable() always returns true, even if the node is
unable to allocate non-CMA memory for the virtual machine.

For costly allocations, because __compaction_suitable() always
returns true, __alloc_pages_slowpath() can't exit at the appropriate
place, resulting in excessively long virtual machine startup times.
Call trace:
__alloc_pages_slowpath
    if (compact_result == COMPACT_SKIPPED ||
        compact_result == COMPACT_DEFERRED)
        goto nopage; // should exit __alloc_pages_slowpath() from here

To sum up, during long term GUP flow, we should remove ALLOC_CMA
both in __compaction_suitable() and __isolate_free_page().

Signed-off-by: yangge <[e-mail]>
---

V3:
- fix build errors
- add ALLOC_CMA both in should_continue_reclaim() and compaction_ready()

V2:
- using the 'cc->alloc_flags' to determin if 'ALLOC_CMA' is needed
- rich the commit log description

 include/linux/compaction.h |  6 ++++--
 mm/compaction.c            | 18 +++++++++++-------
 mm/page_alloc.c            |  4 +++-
 mm/vmscan.c                |  4 ++--
 4 files changed, 20 insertions(+), 12 deletions(-)

Patch

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index e947764..b4c3ac3 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -90,7 +90,8 @@  extern enum compact_result try_to_compact_pages(gfp_t gfp_mask,
 		struct page **page);
 extern void reset_isolation_suitable(pg_data_t *pgdat);
 extern bool compaction_suitable(struct zone *zone, int order,
-					       int highest_zoneidx);
+					       int highest_zoneidx,
+					       unsigned int alloc_flags);
 
 extern void compaction_defer_reset(struct zone *zone, int order,
 				bool alloc_success);
@@ -108,7 +109,8 @@  static inline void reset_isolation_suitable(pg_data_t *pgdat)
 }
 
 static inline bool compaction_suitable(struct zone *zone, int order,
-						      int highest_zoneidx)
+						      int highest_zoneidx,
+						      unsigned int alloc_flags)
 {
 	return false;
 }
diff --git a/mm/compaction.c b/mm/compaction.c
index 07bd227..585f5ab 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2381,9 +2381,11 @@  static enum compact_result compact_finished(struct compact_control *cc)
 
 static bool __compaction_suitable(struct zone *zone, int order,
 				  int highest_zoneidx,
+				  unsigned int alloc_flags,
 				  unsigned long wmark_target)
 {
 	unsigned long watermark;
+	bool use_cma;
 	/*
 	 * Watermarks for order-0 must be met for compaction to be able to
 	 * isolate free pages for migration targets. This means that the
@@ -2395,25 +2397,27 @@  static bool __compaction_suitable(struct zone *zone, int order,
 	 * even if compaction succeeds.
 	 * For costly orders, we require low watermark instead of min for
 	 * compaction to proceed to increase its chances.
-	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
-	 * suitable migration targets
+	 * In addition to long term GUP flow, ALLOC_CMA is used, as pages in
+	 * CMA pageblocks are considered suitable migration targets
 	 */
 	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
 				low_wmark_pages(zone) : min_wmark_pages(zone);
 	watermark += compact_gap(order);
+	use_cma = !!(alloc_flags & ALLOC_CMA);
 	return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
-				   ALLOC_CMA, wmark_target);
+				   use_cma ? ALLOC_CMA : 0, wmark_target);
 }
 
 /*
  * compaction_suitable: Is this suitable to run compaction on this zone now?
  */
-bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx)
+bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx,
+				   unsigned int alloc_flags)
 {
 	enum compact_result compact_result;
 	bool suitable;
 
-	suitable = __compaction_suitable(zone, order, highest_zoneidx,
+	suitable = __compaction_suitable(zone, order, highest_zoneidx, alloc_flags,
 					 zone_page_state(zone, NR_FREE_PAGES));
 	/*
 	 * fragmentation index determines if allocation failures are due to
@@ -2474,7 +2478,7 @@  bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 		available = zone_reclaimable_pages(zone) / order;
 		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
 		if (__compaction_suitable(zone, order, ac->highest_zoneidx,
-					  available))
+					  alloc_flags, available))
 			return true;
 	}
 
@@ -2499,7 +2503,7 @@  compaction_suit_allocation_order(struct zone *zone, unsigned int order,
 			      alloc_flags))
 		return COMPACT_SUCCESS;
 
-	if (!compaction_suitable(zone, order, highest_zoneidx))
+	if (!compaction_suitable(zone, order, highest_zoneidx, alloc_flags))
 		return COMPACT_SKIPPED;
 
 	return COMPACT_CONTINUE;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dde19db..9a5dfda 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2813,6 +2813,7 @@  int __isolate_free_page(struct page *page, unsigned int order)
 {
 	struct zone *zone = page_zone(page);
 	int mt = get_pageblock_migratetype(page);
+	bool pin;
 
 	if (!is_migrate_isolate(mt)) {
 		unsigned long watermark;
@@ -2823,7 +2824,8 @@  int __isolate_free_page(struct page *page, unsigned int order)
 		 * exists.
 		 */
 		watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
-		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
+		pin = !!(current->flags & PF_MEMALLOC_PIN);
+		if (!zone_watermark_ok(zone, 0, watermark, 0, pin ? 0 : ALLOC_CMA))
 			return 0;
 	}
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5e03a61..33f5b46 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5815,7 +5815,7 @@  static inline bool should_continue_reclaim(struct pglist_data *pgdat,
 				      sc->reclaim_idx, 0))
 			return false;
 
-		if (compaction_suitable(zone, sc->order, sc->reclaim_idx))
+		if (compaction_suitable(zone, sc->order, sc->reclaim_idx, ALLOC_CMA))
 			return false;
 	}
 
@@ -6043,7 +6043,7 @@  static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
 		return true;
 
 	/* Compaction cannot yet proceed. Do reclaim. */
-	if (!compaction_suitable(zone, sc->order, sc->reclaim_idx))
+	if (!compaction_suitable(zone, sc->order, sc->reclaim_idx, ALLOC_CMA))
 		return false;
 
 	/*