Re: [PATCH v3 09/14] mm, page_owner: print migratetype of page and pageblock, symbolic flags

[Michal Hocko <mhocko@kernel.org>]

On Fri 18-12-15 10:03:21, Vlastimil Babka wrote:
> The information in /sys/kernel/debug/page_owner includes the migratetype of
> the pageblock the page belongs to. This is also checked against the page's
> migratetype (as declared by gfp_flags during its allocation), and the page is
> reported as Fallback if its migratetype differs from the pageblock's one.
> t
> This is somewhat misleading because in fact fallback allocation is not the only
> reason why these two can differ. It also doesn't direcly provide the page's
> migratetype, although it's possible to derive that from the gfp_flags.
> 
> It's arguably better to print both page and pageblock's migratetype and leave
> the interpretation to the consumer than to suggest fallback allocation as the
> only possible reason. While at it, we can print the migratetypes as string
> the same way as /proc/pagetypeinfo does, as some of the numeric values depend
> on kernel configuration. For that, this patch moves the migratetype_names
> array from #ifdef CONFIG_PROC_FS part of mm/vmstat.c to mm/page_alloc.c and
> exports it.
> 
> With the new format strings for flags, we can now also provide symbolic page
> and gfp flags in the /sys/kernel/debug/page_owner file. This replaces the
> positional printing of page flags as single letters, which might have looked
> nicer, but was limited to a subset of flags, and required the user to remember
> the letters.
> 
> Example page_owner entry after the patch:
> 
> Page allocated via order 0, mask 0x24213ca(GFP_HIGHUSER_MOVABLE|GFP_COLD|GFP_NOWARN|GFP_NORETRY)
> PFN 674308 type Movable Block 1317 type Movable Flags 0x1fffff80010068(uptodate|lru|active|mappedtodisk)
>  [<ffffffff81164e9a>] __alloc_pages_nodemask+0x15a/0xa30
>  [<ffffffff811ab938>] alloc_pages_current+0x88/0x120
>  [<ffffffff8115bc46>] __page_cache_alloc+0xe6/0x120
>  [<ffffffff81168b9b>] __do_page_cache_readahead+0xdb/0x200
>  [<ffffffff81168df5>] ondemand_readahead+0x135/0x260
>  [<ffffffff81168f8c>] page_cache_async_readahead+0x6c/0x70
>  [<ffffffff8115d5f8>] generic_file_read_iter+0x378/0x590
>  [<ffffffff811d12a7>] __vfs_read+0xa7/0xd0
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michal Hocko <mhocko@suse.cz>

Looks good to me
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
>  include/linux/mmzone.h |  3 +++
>  mm/page_alloc.c        | 13 +++++++++++++
>  mm/page_owner.c        | 24 +++++++-----------------
>  mm/vmstat.c            | 13 -------------
>  4 files changed, 23 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 33bb1b19273e..68cc063bf0b7 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -63,6 +63,9 @@ enum {
>  	MIGRATE_TYPES
>  };
>  
> +/* In mm/page_alloc.c; keep in sync also with show_migration_types() there */
> +extern char * const migratetype_names[MIGRATE_TYPES];
> +
>  #ifdef CONFIG_CMA
>  #  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
>  #else
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 08e514721a57..67538b58e478 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -222,6 +222,19 @@ static char * const zone_names[MAX_NR_ZONES] = {
>  #endif
>  };
>  
> +char * const migratetype_names[MIGRATE_TYPES] = {
> +	"Unmovable",
> +	"Movable",
> +	"Reclaimable",
> +	"HighAtomic",
> +#ifdef CONFIG_CMA
> +	"CMA",
> +#endif
> +#ifdef CONFIG_MEMORY_ISOLATION
> +	"Isolate",
> +#endif
> +};
> +
>  compound_page_dtor * const compound_page_dtors[] = {
>  	NULL,
>  	free_compound_page,
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 983c3a10fa07..5392195fca61 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -100,8 +100,9 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		return -ENOMEM;
>  
>  	ret = snprintf(kbuf, count,
> -			"Page allocated via order %u, mask 0x%x\n",
> -			page_ext->order, page_ext->gfp_mask);
> +			"Page allocated via order %u, mask %#x(%pgg)\n",
> +			page_ext->order, page_ext->gfp_mask,
> +			&page_ext->gfp_mask);
>  
>  	if (ret >= count)
>  		goto err;
> @@ -110,23 +111,12 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  	pageblock_mt = get_pfnblock_migratetype(page, pfn);
>  	page_mt  = gfpflags_to_migratetype(page_ext->gfp_mask);
>  	ret += snprintf(kbuf + ret, count - ret,
> -			"PFN %lu Block %lu type %d %s Flags %s%s%s%s%s%s%s%s%s%s%s%s\n",
> +			"PFN %lu type %s Block %lu type %s Flags %#lx(%pgp)\n",
>  			pfn,
> +			migratetype_names[page_mt],
>  			pfn >> pageblock_order,
> -			pageblock_mt,
> -			pageblock_mt != page_mt ? "Fallback" : "        ",
> -			PageLocked(page)	? "K" : " ",
> -			PageError(page)		? "E" : " ",
> -			PageReferenced(page)	? "R" : " ",
> -			PageUptodate(page)	? "U" : " ",
> -			PageDirty(page)		? "D" : " ",
> -			PageLRU(page)		? "L" : " ",
> -			PageActive(page)	? "A" : " ",
> -			PageSlab(page)		? "S" : " ",
> -			PageWriteback(page)	? "W" : " ",
> -			PageCompound(page)	? "C" : " ",
> -			PageSwapCache(page)	? "B" : " ",
> -			PageMappedToDisk(page)	? "M" : " ");
> +			migratetype_names[pageblock_mt],
> +			page->flags, &page->flags);
>  
>  	if (ret >= count)
>  		goto err;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index dfe7315f2db6..475d154411f0 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -924,19 +924,6 @@ static void walk_zones_in_node(struct seq_file *m, pg_data_t *pgdat,
>  #endif
>  
>  #ifdef CONFIG_PROC_FS
> -static char * const migratetype_names[MIGRATE_TYPES] = {
> -	"Unmovable",
> -	"Movable",
> -	"Reclaimable",
> -	"HighAtomic",
> -#ifdef CONFIG_CMA
> -	"CMA",
> -#endif
> -#ifdef CONFIG_MEMORY_ISOLATION
> -	"Isolate",
> -#endif
> -};
> -
>  static void frag_show_print(struct seq_file *m, pg_data_t *pgdat,
>  						struct zone *zone)
>  {
> -- 
> 2.6.3

-- 
Michal Hocko
SUSE Labs