[V5] mm, compaction: don't use ALLOC_CMA in long term GUP flow

Commit Message

Ge Yang Dec. 16, 2024, 11:54 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

In order to quickly fall back to remote node, we should remove
ALLOC_CMA both in __compaction_suitable() and __isolate_free_page()
in long term GUP flow. After this fix, starting a 32GB virtual machine
with device passthrough takes only a few seconds.

Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()")
Cc: <[e-mail]>
Signed-off-by: yangge <[e-mail]>
---

V5:
- add 'alloc_flags' parameter for __isolate_free_page()
- remove 'usa_cma' variable

V4:
- rich the commit log description

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            | 20 +++++++++++---------
 mm/internal.h              |  3 ++-
 mm/page_alloc.c            |  6 ++++--
 mm/page_isolation.c        |  3 ++-
 mm/page_reporting.c        |  2 +-
 mm/vmscan.c                |  4 ++--
 7 files changed, 26 insertions(+), 18 deletions(-)

Comments

Baolin Wang Dec. 17, 2024, 2:35 a.m. UTC | #1

On 2024/12/16 19:54, [e-mail] wrote:
> 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
> 
> In order to quickly fall back to remote node, we should remove
> ALLOC_CMA both in __compaction_suitable() and __isolate_free_page()
> in long term GUP flow. After this fix, starting a 32GB virtual machine
> with device passthrough takes only a few seconds.
> 
> Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()")
> Cc: <[e-mail]>
> Signed-off-by: yangge <[e-mail]>
> ---

I sent a follow-up fix patch[1] to update the cc->alloc_flags, and with 
that, looks good to me.
Reviewed-by: Baolin Wang <[e-mail]>

[1] 
https://lore.kernel.org/all/[e-mail]/

Ge Yang Dec. 17, 2024, 3:32 a.m. UTC | #2

在 2024/12/17 10:35, Baolin Wang 写道:
> 
> 
> On 2024/12/16 19:54, [e-mail] wrote:
>> 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
>>
>> In order to quickly fall back to remote node, we should remove
>> ALLOC_CMA both in __compaction_suitable() and __isolate_free_page()
>> in long term GUP flow. After this fix, starting a 32GB virtual machine
>> with device passthrough takes only a few seconds.
>>
>> Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in 
>> __compaction_suitable()")
>> Cc: <[e-mail]>
>> Signed-off-by: yangge <[e-mail]>
>> ---
> 
> I sent a follow-up fix patch[1] to update the cc->alloc_flags, and with 
> that, looks good to me.
> Reviewed-by: Baolin Wang <[e-mail]>
> 
> [1] 
> https://lore.kernel.org/all/[e-mail]/
Thanks

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..b10d921 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -655,7 +655,7 @@  static unsigned long isolate_freepages_block(struct compact_control *cc,
 
 		/* Found a free page, will break it into order-0 pages */
 		order = buddy_order(page);
-		isolated = __isolate_free_page(page, order);
+		isolated = __isolate_free_page(page, order, cc->alloc_flags);
 		if (!isolated)
 			break;
 		set_page_private(page, order);
@@ -1634,7 +1634,7 @@  static void fast_isolate_freepages(struct compact_control *cc)
 
 		/* Isolate the page if available */
 		if (page) {
-			if (__isolate_free_page(page, order)) {
+			if (__isolate_free_page(page, order, cc->alloc_flags)) {
 				set_page_private(page, order);
 				nr_isolated = 1 << order;
 				nr_scanned += nr_isolated - 1;
@@ -2381,6 +2381,7 @@  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;
@@ -2395,25 +2396,26 @@  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);
 	return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
-				   ALLOC_CMA, wmark_target);
+				   alloc_flags & ALLOC_CMA, 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 +2476,7 @@  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 +2501,7 @@  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/internal.h b/mm/internal.h
index 3922788..6d257c8 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -662,7 +662,8 @@  static inline void clear_zone_contiguous(struct zone *zone)
 	zone->contiguous = false;
 }
 
-extern int __isolate_free_page(struct page *page, unsigned int order);
+extern int __isolate_free_page(struct page *page, unsigned int order,
+				    unsigned int alloc_flags);
 extern void __putback_isolated_page(struct page *page, unsigned int order,
 				    int mt);
 extern void memblock_free_pages(struct page *page, unsigned long pfn,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dde19db..ecb2fd7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2809,7 +2809,8 @@  void split_page(struct page *page, unsigned int order)
 }
 EXPORT_SYMBOL_GPL(split_page);
 
-int __isolate_free_page(struct page *page, unsigned int order)
+int __isolate_free_page(struct page *page, unsigned int order,
+				   unsigned int alloc_flags)
 {
 	struct zone *zone = page_zone(page);
 	int mt = get_pageblock_migratetype(page);
@@ -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))
+		if (!zone_watermark_ok(zone, 0, watermark, 0,
+			    alloc_flags & ALLOC_CMA))
 			return 0;
 	}
 
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c608e9d..a1f2c79 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -229,7 +229,8 @@  static void unset_migratetype_isolate(struct page *page, int migratetype)
 			buddy = find_buddy_page_pfn(page, page_to_pfn(page),
 						    order, NULL);
 			if (buddy && !is_migrate_isolate_page(buddy)) {
-				isolated_page = !!__isolate_free_page(page, order);
+				isolated_page = !!__isolate_free_page(page, order,
+						    ALLOC_CMA);
 				/*
 				 * Isolating a free page in an isolated pageblock
 				 * is expected to always work as watermarks don't
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index e4c428e..fd3813b 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -198,7 +198,7 @@  page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 
 		/* Attempt to pull page from list and place in scatterlist */
 		if (*offset) {
-			if (!__isolate_free_page(page, order)) {
+			if (!__isolate_free_page(page, order, ALLOC_CMA)) {
 				next = page;
 				break;
 			}
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;
 
 	/*