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From: Yosry Ahmed To: Sergey Senozhatsky Cc: Andrew Morton , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 11/17] zsmalloc: make zspage lock preemptible Message-ID: References: <20250221093832.1949691-1-senozhatsky@chromium.org> <20250221093832.1949691-12-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250221093832.1949691-12-senozhatsky@chromium.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 20C874000D X-Stat-Signature: 3nkepp1n6s4pto3cwetpuhatkyabuiiy X-Rspam-User: X-HE-Tag: 1740167316-403716 X-HE-Meta: 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 WixBa0af R/EvXAgnPsYjVXb36FtqJ3dBRPgqlFaE8+scPmRvanTxMy4FVtNN1j3FuziBecnBkT9q7e62ayNpeXyHSoDbFUTfIkmC25+sircoamMd1bI7uZK43taN8e3AmbS94dHRp10DIOj1q6SKH0PgQUlIviaiqVrk7RZiAu/hK8nJYOtgh216aNcObBmYuVo3fJQF/xvbW/pknn15Ni0C1fJPx+gypWuxp/QD+jRGcKXmjjOe8HFcLOit2QRgSdaGD6fDCJG4A 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: List-Subscribe: List-Unsubscribe: On Fri, Feb 21, 2025 at 06:38:04PM +0900, Sergey Senozhatsky wrote: > In order to implement preemptible object mapping we need a zspage lock > that satisfies several preconditions: > - it should be reader-write type of a lock > - it should be possible to hold it from any context, but also being > preemptible if the context allows it > - we never sleep while acquiring but can sleep while holding in read > mode > > An rwsemaphore doesn't suffice, due to atomicity requirements, rwlock > doesn't satisfy due to reader-preemptability requirement. It's also > worth to mention, that per-zspage rwsem is a little too memory heavy > (we can easily have double digits megabytes used only on rwsemaphores). > > Switch over from rwlock_t to a atomic_t-based implementation of a > reader-writer semaphore that satisfies all of the preconditions. > > The spin-lock based zspage_lock is suggested by Hillf Danton. > > Suggested-by: Hillf Danton > Signed-off-by: Sergey Senozhatsky > --- > mm/zsmalloc.c | 189 +++++++++++++++++++++++++++++++++++--------------- > 1 file changed, 135 insertions(+), 54 deletions(-) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 1424ee73cbb5..250f1fddaf34 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -226,6 +226,9 @@ struct zs_pool { > /* protect zspage migration/compaction */ > rwlock_t lock; > atomic_t compaction_in_progress; > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > + struct lock_class_key lock_class; > +#endif > }; > > static inline void zpdesc_set_first(struct zpdesc *zpdesc) > @@ -257,6 +260,18 @@ static inline void free_zpdesc(struct zpdesc *zpdesc) > __free_page(page); > } > > +#define ZS_PAGE_UNLOCKED 0 > +#define ZS_PAGE_WRLOCKED -1 > + > +struct zspage_lock { > + spinlock_t lock; > + int cnt; > + > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > + struct lockdep_map dep_map; > +#endif > +}; > + > struct zspage { > struct { > unsigned int huge:HUGE_BITS; > @@ -269,7 +284,7 @@ struct zspage { > struct zpdesc *first_zpdesc; > struct list_head list; /* fullness list */ > struct zs_pool *pool; > - rwlock_t lock; > + struct zspage_lock zsl; > }; > > struct mapping_area { > @@ -279,6 +294,91 @@ struct mapping_area { > enum zs_mapmode vm_mm; /* mapping mode */ > }; > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > +#define zsl_dep_map(zsl) (&(zsl)->dep_map) > +#else > +#define zsl_dep_map(zsl) NULL > +#endif > + > +static void zspage_lock_init(struct zspage *zspage) > +{ > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > + lockdep_init_map(&zspage->zsl.dep_map, "zspage->lock", > + &zspage->pool->lock_class, 0); Can't we remove this #ifdef as well by adding a similar macro? (e.g. zsl_lock_class())