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Subject: Re: [PATCH V4] mm/vmstat: Add events for THP migration without split
To:     Anshuman Khandual <anshuman.khandual@arm.com>, linux-mm@kvack.org
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Hugh Dickins <hughd@google.com>,
        Matthew Wilcox <willy@infradead.org>, Zi Yan <ziy@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1594287583-16568-1-git-send-email-anshuman.khandual@arm.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <cab90a5c-4c61-e9ad-659f-a9438d639fe5@infradead.org>
Date:   Thu, 9 Jul 2020 08:34:37 -0700
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Hi,

I have a few comments on this.

a. I reported it very early and should have been Cc-ed.

b. A patch that applies to mmotm or linux-next would have been better
than a full replacement patch.

c. I tried replacing what I believe is the correct/same patch file in mmotm
and still have build errors.

(more below)

On 7/9/20 2:39 AM, Anshuman Khandual wrote:

> ---
> Applies on 5.8-rc4.
> 
> Changes in V4:
> 
> - Changed THP_MIGRATION_FAILURE as THP_MIGRATION_FAIL per John
> - Dropped all conditional 'if' blocks in migrate_pages() per Andrew and John
> - Updated migration events documentation per John
> - Updated thp_nr_pages variable as nr_subpages for an expected merge conflict
> - Moved all new THP vmstat events into CONFIG_MIGRATION
> - Updated Cc list with Documentation/ and tracing related addresses
> 
> Changes in V3: (https://patchwork.kernel.org/patch/11647237/)
> 
> - Formatted new events documentation with 'fmt' tool per Matthew
> - Made events universally available i.e dropped ARCH_ENABLE_THP_MIGRATION
> - Added THP_MIGRATION_SPLIT
> - Updated trace_mm_migrate_pages() with THP events
> - Made THP events update normal page migration events as well
> 
> Changes in V2: (https://patchwork.kernel.org/patch/11586893/)
> 
> - Dropped PMD reference both from code and commit message per Matthew
> - Added documentation and updated the commit message per Daniel
> 
> Changes in V1: (https://patchwork.kernel.org/patch/11564497/)
> 
> - Changed function name as thp_pmd_migration_success() per John
> - Folded in a fix (https://patchwork.kernel.org/patch/11563009/) from Hugh
> 
> Changes in RFC V2: (https://patchwork.kernel.org/patch/11554861/)
> 
> - Decopupled and renamed VM events from their implementation per Zi and John
> - Added THP_PMD_MIGRATION_FAILURE VM event upon allocation failure and split
> 
> Changes in RFC V1: (https://patchwork.kernel.org/patch/11542055/)
> 
>  Documentation/vm/page_migration.rst | 27 +++++++++++++++
>  include/linux/vm_event_item.h       |  3 ++
>  include/trace/events/migrate.h      | 17 ++++++++--
>  mm/migrate.c                        | 52 ++++++++++++++++++++++++-----
>  mm/vmstat.c                         |  3 ++
>  5 files changed, 91 insertions(+), 11 deletions(-)
> 

> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 24fc7c3ae7d6..2e6ca53b9bbd 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -56,6 +56,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  #endif
>  #ifdef CONFIG_MIGRATION
>  		PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
> +		THP_MIGRATION_SUCCESS,
> +		THP_MIGRATION_FAIL,
> +		THP_MIGRATION_SPLIT,

These 3 new symbols are still only present if CONFIG_MIGRATION=y, but the build errors
are using these symbols even when CONFIG_MIGRATION is not set.

>  #endif
>  #ifdef CONFIG_COMPACTION
>  		COMPACTMIGRATE_SCANNED, COMPACTFREE_SCANNED,

> diff --git a/mm/migrate.c b/mm/migrate.c
> index f37729673558..c706e3576cfc 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1429,22 +1429,35 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  		enum migrate_mode mode, int reason)
>  {
>  	int retry = 1;
> +	int thp_retry = 1;
>  	int nr_failed = 0;
>  	int nr_succeeded = 0;
> +	int nr_thp_succeeded = 0;
> +	int nr_thp_failed = 0;
> +	int nr_thp_split = 0;
>  	int pass = 0;
> +	bool is_thp = false;
>  	struct page *page;
>  	struct page *page2;
>  	int swapwrite = current->flags & PF_SWAPWRITE;
> -	int rc;
> +	int rc, nr_subpages;
>  
>  	if (!swapwrite)
>  		current->flags |= PF_SWAPWRITE;
>  
> -	for(pass = 0; pass < 10 && retry; pass++) {
> +	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
>  		retry = 0;
> +		thp_retry = 0;
>  
>  		list_for_each_entry_safe(page, page2, from, lru) {
>  retry:
> +			/*
> +			 * THP statistics is based on the source huge page.
> +			 * Capture required information that might get lost
> +			 * during migration.
> +			 */
> +			is_thp = PageTransHuge(page);
> +			nr_subpages = hpage_nr_pages(page);
>  			cond_resched();
>  
>  			if (PageHuge(page))
> @@ -1475,15 +1488,30 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  					unlock_page(page);
>  					if (!rc) {
>  						list_safe_reset_next(page, page2, lru);
> +						nr_thp_split++;
>  						goto retry;
>  					}
>  				}
> +				if (is_thp) {
> +					nr_thp_failed++;
> +					nr_failed += nr_subpages;
> +					goto out;
> +				}
>  				nr_failed++;
>  				goto out;
>  			case -EAGAIN:
> +				if (is_thp) {
> +					thp_retry++;
> +					break;
> +				}
>  				retry++;
>  				break;
>  			case MIGRATEPAGE_SUCCESS:
> +				if (is_thp) {
> +					nr_thp_succeeded++;
> +					nr_succeeded += nr_subpages;
> +					break;
> +				}
>  				nr_succeeded++;
>  				break;
>  			default:
> @@ -1493,19 +1521,27 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  				 * removed from migration page list and not
>  				 * retried in the next outer loop.
>  				 */
> +				if (is_thp) {
> +					nr_thp_failed++;
> +					nr_failed += nr_subpages;
> +					break;
> +				}
>  				nr_failed++;
>  				break;
>  			}
>  		}
>  	}
> -	nr_failed += retry;
> +	nr_failed += retry + thp_retry;
> +	nr_thp_failed += thp_retry;
>  	rc = nr_failed;
>  out:
> -	if (nr_succeeded)
> -		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
> -	if (nr_failed)
> -		count_vm_events(PGMIGRATE_FAIL, nr_failed);
> -	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
> +	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
> +	count_vm_events(PGMIGRATE_FAIL, nr_failed);
> +	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
> +	count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
> +	count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);

These references still cause build errors.

> +	trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,
> +			       nr_thp_failed, nr_thp_split, mode, reason);
>  
>  	if (!swapwrite)
>  		current->flags &= ~PF_SWAPWRITE;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 3fb23a21f6dd..09914a4bfee4 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1234,6 +1234,9 @@ const char * const vmstat_text[] = {
>  #ifdef CONFIG_MIGRATION
>  	"pgmigrate_success",
>  	"pgmigrate_fail",
> +	"thp_migration_success",
> +	"thp_migration_fail",
> +	"thp_migration_split",
>  #endif
>  #ifdef CONFIG_COMPACTION
>  	"compact_migrate_scanned",
> 


-- 
~Randy