linux-kernel - Re: [PATCH 6/6] mm/gup: migrate pinned pages out of movable zone

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Date:   Fri, 4 Dec 2020 13:13:59 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, vbabka@...e.cz, mhocko@...e.com,
        david@...hat.com, osalvador@...e.de, dan.j.williams@...el.com,
        sashal@...nel.org, tyhicks@...ux.microsoft.com,
        mike.kravetz@...cle.com, rostedt@...dmis.org, mingo@...hat.com,
        jgg@...pe.ca, peterz@...radead.org, mgorman@...e.de,
        willy@...radead.org, rientjes@...gle.com, jhubbard@...dia.com
Subject: Re: [PATCH 6/6] mm/gup: migrate pinned pages out of movable zone

On Wed, Dec 02, 2020 at 12:23:30AM -0500, Pavel Tatashin wrote:
> We do not allocate pin pages in ZONE_MOVABLE, but if pages were already
> allocated before pinning they need to migrated to a different zone.
> Currently, we migrate movable CMA pages only. Generalize the function
> that migrates CMA pages to migrate all movable pages.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> ---
>  include/linux/migrate.h        |  1 +
>  include/trace/events/migrate.h |  3 +-
>  mm/gup.c                       | 56 +++++++++++++---------------------
>  3 files changed, 24 insertions(+), 36 deletions(-)
> 
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 0f8d1583fa8e..00bab23d1ee5 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -27,6 +27,7 @@ enum migrate_reason {
>  	MR_MEMPOLICY_MBIND,
>  	MR_NUMA_MISPLACED,
>  	MR_CONTIG_RANGE,
> +	MR_LONGTERM_PIN,
>  	MR_TYPES
>  };
>  
> diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
> index 4d434398d64d..363b54ce104c 100644
> --- a/include/trace/events/migrate.h
> +++ b/include/trace/events/migrate.h
> @@ -20,7 +20,8 @@
>  	EM( MR_SYSCALL,		"syscall_or_cpuset")		\
>  	EM( MR_MEMPOLICY_MBIND,	"mempolicy_mbind")		\
>  	EM( MR_NUMA_MISPLACED,	"numa_misplaced")		\
> -	EMe(MR_CONTIG_RANGE,	"contig_range")
> +	EM( MR_CONTIG_RANGE,	"contig_range")			\
> +	EMe(MR_LONGTERM_PIN,	"longterm_pin")
>  
>  /*
>   * First define the enums in the above macros to be exported to userspace
> diff --git a/mm/gup.c b/mm/gup.c
> index 724d8a65e1df..1d511f65f8a7 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1593,19 +1593,18 @@ static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>  }
>  #endif
>  
> -#ifdef CONFIG_CMA
> -static long check_and_migrate_cma_pages(struct mm_struct *mm,
> -					unsigned long start,
> -					unsigned long nr_pages,
> -					struct page **pages,
> -					struct vm_area_struct **vmas,
> -					unsigned int gup_flags)
> +static long check_and_migrate_movable_pages(struct mm_struct *mm,
> +					    unsigned long start,
> +					    unsigned long nr_pages,
> +					    struct page **pages,
> +					    struct vm_area_struct **vmas,
> +					    unsigned int gup_flags)
>  {
>  	unsigned long i;
>  	unsigned long step;
>  	bool drain_allow = true;
>  	bool migrate_allow = true;
> -	LIST_HEAD(cma_page_list);
> +	LIST_HEAD(page_list);
>  	long ret = nr_pages;
>  	struct migration_target_control mtc = {
>  		.nid = NUMA_NO_NODE,
> @@ -1623,13 +1622,12 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
>  		 */
>  		step = compound_nr(head) - (pages[i] - head);
>  		/*
> -		 * If we get a page from the CMA zone, since we are going to
> -		 * be pinning these entries, we might as well move them out
> -		 * of the CMA zone if possible.
> +		 * If we get a movable page, since we are going to be pinning
> +		 * these entries, try to move them out if possible.
>  		 */
> -		if (is_migrate_cma_page(head)) {
> +		if (is_migrate_movable(get_pageblock_migratetype(head))) {

is_migrate_movable() isn't a check for the ZONE. It's a check for the
MIGRATE_TYPE. MIGRATE_TYPE doesn't require hard guarantee for
migration, and, most of memory, including ZONE_NORMAL, is
MIGRATE_MOVABLE. With this code, long term gup would always fails due
to not enough memory. I think that correct change would be
"is_migrate_cma_page(hear) && zone == ZONE_MOVABLE".

Patch #5 also has this problem. Please fix it too.

Thanks.