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Tue, 18 Apr 2023 12:49:42 -0700 (PDT) MIME-Version: 1.0 References: <20230418074639.1903197-1-senozhatsky@chromium.org> In-Reply-To: <20230418074639.1903197-1-senozhatsky@chromium.org> From: Yosry Ahmed Date: Tue, 18 Apr 2023 12:49:04 -0700 Message-ID: Subject: Re: [PATCHv3] zsmalloc: allow only one active pool compaction context To: Sergey Senozhatsky Cc: Minchan Kim , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 7E4C740014 X-Stat-Signature: dbkqsa6j7ygo1ky6gsiinja7oezqeg7i X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1681847384-289594 X-HE-Meta: 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 666dEbtO uNXDSAfDTR2QI+vtQhifI2kkIxWarCVqqFd7NJqkzJsXT5mPAdhGSSxAOSAQe6yPnEIn8psAjTI/ElmiFQmneeupdBL98odTFtN9G6CyPBkWFXyBmHYN7sokMHlINnu4GqF4yG6jJqmoMGF20m7wCNGPucqmAPrDDxmb8bDlYSv0W5trZUFzgDswVsPjXlSw507AuU1TrRvPFL8zamCs3KofTsfGo8CLsJFGgNtPlH4x0YcsT3OcqpbMd5uBhQVEfz+G7e0W5zfGbpXbn8iXaeorzvlpnTCopsvyqJ9WCgbU97FQI7onVjORK8v4q6WL/4nf5RFnjVgBeJbqHs/BkuUbNz7RgQMoOCHOyodwZCyUOnFr0QCQwM4w63g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 18, 2023 at 12:46=E2=80=AFAM Sergey Senozhatsky wrote: > > zsmalloc pool can be compacted concurrently by many contexts, > e.g. > > cc1 handle_mm_fault() > do_anonymous_page() > __alloc_pages_slowpath() > try_to_free_pages() > do_try_to_free_pages( > lru_gen_shrink_node() > shrink_slab() > do_shrink_slab() > zs_shrinker_scan() > zs_compact() > > Pool compaction is currently (basically) single-threaded as > it is performed under pool->lock. Having multiple compaction > threads results in unnecessary contention, as each thread > competes for pool->lock. This, in turn, affects all zsmalloc > operations such as zs_malloc(), zs_map_object(), zs_free(), etc. > > Introduce the pool->compaction_in_progress atomic variable, > which ensures that only one compaction context can run at a > time. This reduces overall pool->lock contention in (corner) > cases when many contexts attempt to shrink zspool simultaneously. > > Fixes: c0547d0b6a4b ("zsmalloc: consolidate zs_pool's migrate_lock and si= ze_class's locks") > Signed-off-by: Sergey Senozhatsky Reviewed-by: Yosry Ahmed > --- > mm/zsmalloc.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index cc81dfba05a0..44ddaf5d601e 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -264,6 +264,7 @@ struct zs_pool { > struct work_struct free_work; > #endif > spinlock_t lock; > + atomic_t compaction_in_progress; > }; > > struct zspage { > @@ -2274,6 +2275,15 @@ unsigned long zs_compact(struct zs_pool *pool) > struct size_class *class; > unsigned long pages_freed =3D 0; > > + /* > + * Pool compaction is performed under pool->lock so it is basical= ly > + * single-threaded. Having more than one thread in __zs_compact() > + * will increase pool->lock contention, which will impact other > + * zsmalloc operations that need pool->lock. > + */ > + if (atomic_xchg(&pool->compaction_in_progress, 1)) > + return 0; > + > for (i =3D ZS_SIZE_CLASSES - 1; i >=3D 0; i--) { > class =3D pool->size_class[i]; > if (class->index !=3D i) > @@ -2281,6 +2291,7 @@ unsigned long zs_compact(struct zs_pool *pool) > pages_freed +=3D __zs_compact(pool, class); > } > atomic_long_add(pages_freed, &pool->stats.pages_compacted); > + atomic_set(&pool->compaction_in_progress, 0); > > return pages_freed; > } > @@ -2388,6 +2399,7 @@ struct zs_pool *zs_create_pool(const char *name) > > init_deferred_free(pool); > spin_lock_init(&pool->lock); > + atomic_set(&pool->compaction_in_progress, 0); > > pool->name =3D kstrdup(name, GFP_KERNEL); > if (!pool->name) > -- > 2.40.0.634.g4ca3ef3211-goog >