[PATCH v3 0/8] Fixes and cleanups to compaction

[PATCH v3 0/8] Fixes and cleanups to compaction

[Kemeng Shi]

Hi all, this series contains some random cleanups and fixes to
compation. Details can be found in respective patches.

v2->v3:
-Improve comment in patch 4
-Collect ACK and RVB from David and Baolin.
-Rebase code on current mm-unstable

v1->v2:
-Add comment to skip_offline_sections_reverse in patch 1
-Add impact in git message in patch 2
-Correct comment to fast_find_block instead of remove fast_find_block
in patch 4
-Collect RVB from David and Baolin.

Kemeng Shi (8):
  mm/compaction: avoid missing last page block in section after skip
    offline sections
  mm/compaction: correct last_migrated_pfn update in compact_zone
  mm/compaction: skip page block marked skip in
    isolate_migratepages_block
  mm/compaction: correct comment of fast_find_migrateblock in
    isolate_migratepages
  mm/compaction: correct comment of cached migrate pfn update
  mm/compaction: correct comment to complete migration failure
  mm/compaction: remove unnecessary return for void function
  mm/compaction: only set skip flag if cc->no_set_skip_hint is false

 mm/compaction.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

-- 
2.30.0

[PATCH v3 4/8] mm/compaction: correct comment of fast_find_migrateblock in isolate_migratepages

[Kemeng Shi]

After 90ed667c03fe5 ("Revert "Revert "mm/compaction: fix set skip in
fast_find_migrateblock"""), we remove skip set in fast_find_migrateblock.
Correct comment that fast_find_block is used to avoid isolation_suitable
check for pageblock returned from fast_find_migrateblock because
fast_find_migrateblock will mark found pageblock skipped.
Instead, comment that fast_find_block is used to avoid a redundant check
of fast found pageblock which is already checked skip flag inside
fast_find_migrateblock.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 mm/compaction.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 9a2f0bd5394a..4bf2dc936add 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1988,9 +1988,9 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
 		block_start_pfn = cc->zone->zone_start_pfn;
 
 	/*
-	 * fast_find_migrateblock marks a pageblock skipped so to avoid
-	 * the isolation_suitable check below, check whether the fast
-	 * search was successful.
+	 * fast_find_migrateblock() has already ensured the pageblock is not
+	 * set with a skipped flag, so to avoid the isolation_suitable check
+	 * below again, check whether the fast search was successful.
 	 */
 	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
 
-- 
2.30.0

Re: [PATCH v3 4/8] mm/compaction: correct comment of fast_find_migrateblock in isolate_migratepages

[Baolin Wang]

On 8/4/2023 7:04 PM, Kemeng Shi wrote:
> After 90ed667c03fe5 ("Revert "Revert "mm/compaction: fix set skip in
> fast_find_migrateblock"""), we remove skip set in fast_find_migrateblock.
> Correct comment that fast_find_block is used to avoid isolation_suitable
> check for pageblock returned from fast_find_migrateblock because
> fast_find_migrateblock will mark found pageblock skipped.
> Instead, comment that fast_find_block is used to avoid a redundant check
> of fast found pageblock which is already checked skip flag inside
> fast_find_migrateblock.
> 
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> ---
>   mm/compaction.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 9a2f0bd5394a..4bf2dc936add 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1988,9 +1988,9 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
>   		block_start_pfn = cc->zone->zone_start_pfn;
>   
>   	/*
> -	 * fast_find_migrateblock marks a pageblock skipped so to avoid
> -	 * the isolation_suitable check below, check whether the fast
> -	 * search was successful.
> +	 * fast_find_migrateblock() has already ensured the pageblock is not
> +	 * set with a skipped flag, so to avoid the isolation_suitable check
> +	 * below again, check whether the fast search was successful.
>   	 */
>   	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
>   

[PATCH v3 5/8] mm/compaction: correct comment of cached migrate pfn update

[Kemeng Shi]

Commit e380bebe47715 ("mm, compaction: keep migration source private to
a single compaction instance") moved update of async and sync
compact_cached_migrate_pfn from update_pageblock_skip to
update_cached_migrate but left the comment behind.
Move the relevant comment to correct this.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 4bf2dc936add..fda61dc40f93 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -469,6 +469,7 @@ static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 
 	pfn = pageblock_end_pfn(pfn);
 
+	/* Update where async and sync compaction should restart */
 	if (pfn > zone->compact_cached_migrate_pfn[0])
 		zone->compact_cached_migrate_pfn[0] = pfn;
 	if (cc->mode != MIGRATE_ASYNC &&
@@ -490,7 +491,6 @@ static void update_pageblock_skip(struct compact_control *cc,
 
 	set_pageblock_skip(page);
 
-	/* Update where async and sync compaction should restart */
 	if (pfn < zone->compact_cached_free_pfn)
 		zone->compact_cached_free_pfn = pfn;
 }
-- 
2.30.0

[PATCH v3 6/8] mm/compaction: correct comment to complete migration failure

[Kemeng Shi]

Commit cfccd2e63e7e0 ("mm, compaction: finish pageblocks on complete
migration failure") convert cc->order aligned check to page block
order aligned check. Correct comment relevant with it.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index fda61dc40f93..9022209b64c3 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2534,7 +2534,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			}
 			/*
 			 * If an ASYNC or SYNC_LIGHT fails to migrate a page
-			 * within the current order-aligned block and
+			 * within the pageblock_order-aligned block and
 			 * fast_find_migrateblock may be used then scan the
 			 * remainder of the pageblock. This will mark the
 			 * pageblock "skip" to avoid rescanning in the near
-- 
2.30.0

Re: [PATCH v3 1/8] mm/compaction: avoid missing last page block in section after skip offline sections

[Baolin Wang]

On 8/4/2023 7:04 PM, Kemeng Shi wrote:
> skip_offline_sections_reverse will return the last pfn in found online
> section. Then we set block_start_pfn to start of page block which
> contains the last pfn in section. Then we continue, move one page
> block forward and ignore the last page block in the online section.
> Make block_start_pfn point to first page block after online section to fix
> this:
> 1. make skip_offline_sections_reverse return end pfn of online section,
> i.e. pfn of page block after online section.
> 2. assign block_start_pfn with next_pfn.
> 
> Fixes: f63224525309 ("mm: compaction: skip the memory hole rapidly when isolating free pages")

Again, the Fixes tag is not stable. Please consider squashing it into 
the original commit or hold this patch until the original patch is 
merged into mm-stable branch.

Andrew,
What do you prefer? Thanks.

> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> 
> ---
>   mm/compaction.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 006fc35bffa1..a21b834c5898 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -250,6 +250,11 @@ static unsigned long skip_offline_sections(unsigned long start_pfn)
>   	return 0;
>   }
>   
> +/*
> + * If the PFN falls into an offline section, return the end PFN of the
> + * next online section in reverse. If the PFN falls into an online section
> + * or if there is no next online section in reverse, return 0.
> + */
>   static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>   {
>   	unsigned long start_nr = pfn_to_section_nr(start_pfn);
> @@ -259,7 +264,7 @@ static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
>   
>   	while (start_nr-- > 0) {
>   		if (online_section_nr(start_nr))
> -			return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION - 1;
> +			return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION;
>   	}
>   
>   	return 0;
> @@ -1690,8 +1695,7 @@ static void isolate_freepages(struct compact_control *cc)
>   
>   			next_pfn = skip_offline_sections_reverse(block_start_pfn);
>   			if (next_pfn)
> -				block_start_pfn = max(pageblock_start_pfn(next_pfn),
> -						      low_pfn);
> +				block_start_pfn = max(next_pfn, low_pfn);
>   
>   			continue;
>   		}