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Date: Fri, 12 Mar 2021 09:19:51 +0100
From: Michal Hocko <mhocko@...e.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>, joaodias@...gle.com,
surenb@...gle.com, cgoldswo@...eaurora.org, willy@...radead.org,
david@...hat.com, vbabka@...e.cz, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] mm: replace migrate_prep with lru_add_drain_all
On Wed 10-03-21 08:14:27, Minchan Kim wrote:
> Currently, migrate_prep is merely a wrapper of lru_cache_add_all.
> There is not much to gain from having additional abstraction.
>
> Use lru_add_drain_all instead of migrate_prep, which would be more
> descriptive.
>
> note: migrate_prep_local in compaction.c changed into lru_add_drain
> to avoid CPU schedule cost with involving many other CPUs to keep
> keep old behavior.
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
Acked-by: Michal Hocko <mhocko@...e.com>
Btw. that migrate_prep_local likely needs revisiting. I really fail to
see why it is useful. It looks like just in case thing to me. If it is
needed then the comment should be describing why. Something for a
separate patch though.
> ---
> include/linux/migrate.h | 5 -----
> mm/compaction.c | 3 ++-
> mm/mempolicy.c | 4 ++--
> mm/migrate.c | 24 +-----------------------
> mm/page_alloc.c | 2 +-
> mm/swap.c | 5 +++++
> 6 files changed, 11 insertions(+), 32 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 3a389633b68f..6155d97ec76c 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -45,8 +45,6 @@ extern struct page *alloc_migration_target(struct page *page, unsigned long priv
> extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
> extern void putback_movable_page(struct page *page);
>
> -extern void migrate_prep(void);
> -extern void migrate_prep_local(void);
> extern void migrate_page_states(struct page *newpage, struct page *page);
> extern void migrate_page_copy(struct page *newpage, struct page *page);
> extern int migrate_huge_page_move_mapping(struct address_space *mapping,
> @@ -66,9 +64,6 @@ static inline struct page *alloc_migration_target(struct page *page,
> static inline int isolate_movable_page(struct page *page, isolate_mode_t mode)
> { return -EBUSY; }
>
> -static inline int migrate_prep(void) { return -ENOSYS; }
> -static inline int migrate_prep_local(void) { return -ENOSYS; }
> -
> static inline void migrate_page_states(struct page *newpage, struct page *page)
> {
> }
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e04f4476e68e..3be017ececc0 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2319,7 +2319,8 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
> cc->free_pfn, end_pfn, sync);
>
> - migrate_prep_local();
> + /* lru_add_drain_all could be expensive with involving other CPUs */
> + lru_add_drain();
>
> while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
> int err;
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index ab51132547b8..fc024e97be37 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1124,7 +1124,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
> int err = 0;
> nodemask_t tmp;
>
> - migrate_prep();
> + lru_add_drain_all();
>
> mmap_read_lock(mm);
>
> @@ -1323,7 +1323,7 @@ static long do_mbind(unsigned long start, unsigned long len,
>
> if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
>
> - migrate_prep();
> + lru_add_drain_all();
> }
> {
> NODEMASK_SCRATCH(scratch);
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 62b81d5257aa..45f925e10f5a 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -57,28 +57,6 @@
>
> #include "internal.h"
>
> -/*
> - * migrate_prep() needs to be called before we start compiling a list of pages
> - * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
> - * undesirable, use migrate_prep_local()
> - */
> -void migrate_prep(void)
> -{
> - /*
> - * Clear the LRU lists so pages can be isolated.
> - * Note that pages may be moved off the LRU after we have
> - * drained them. Those pages will fail to migrate like other
> - * pages that may be busy.
> - */
> - lru_add_drain_all();
> -}
> -
> -/* Do the necessary work of migrate_prep but not if it involves other CPUs */
> -void migrate_prep_local(void)
> -{
> - lru_add_drain();
> -}
> -
> int isolate_movable_page(struct page *page, isolate_mode_t mode)
> {
> struct address_space *mapping;
> @@ -1769,7 +1747,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> int start, i;
> int err = 0, err1;
>
> - migrate_prep();
> + lru_add_drain_all();
>
> for (i = start = 0; i < nr_pages; i++) {
> const void __user *p;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2e8348936df8..f05a8db741ca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8467,7 +8467,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
> .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
> };
>
> - migrate_prep();
> + lru_add_drain_all();
>
> while (pfn < end || !list_empty(&cc->migratepages)) {
> if (fatal_signal_pending(current)) {
> diff --git a/mm/swap.c b/mm/swap.c
> index 31b844d4ed94..441d1ae1f285 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -729,6 +729,11 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
> }
>
> /*
> + * lru_add_drain_all() usually needs to be called before we start compiling
> + * a list of pages to be migrated using isolate_lru_page(). Note that pages
> + * may be moved off the LRU after we have drained them. Those pages will
> + * fail to migrate like other pages that may be busy.
> + *
> * Doesn't need any cpu hotplug locking because we do rely on per-cpu
> * kworkers being shut down before our page_alloc_cpu_dead callback is
> * executed on the offlined cpu.
> --
> 2.30.1.766.gb4fecdf3b7-goog
--
Michal Hocko
SUSE Labs
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