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bh=ELrdWh+oiwPySUmNrNaw3uaqbpSpzCG+QNVPa7a0NZY=; b=Ou+OCzDtQy/UJN3MlgDXH8vRE9gtAa0/4VaNdpcnVt3mMkPqKD+6q5mG9WsHVHGiCE0sR+ LILy5jG/HP5lkomfk+V3ACESDlTUD2hX2EguIeSdQvlaWMvbqH43+esckOdkvncptcYLHT DwZ7GuuUaiylAyUa/DVAcZL+59JwFNROR/QVf90DpRyOc9rr3/MXmwc7syoUJUntHY6CS6 HkQ0j/6sRJh59gvbWIZHHeqGGK5rMw+U+QClB71GLRQegILWF7aEHopH+3UamXMz936x/o Nf4DeRaheJnIpRVgPvTbkRIXdMiQLMp8i6G3dcoyDDM19RMT9tJ4Mu//OUGR3A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740387585; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ELrdWh+oiwPySUmNrNaw3uaqbpSpzCG+QNVPa7a0NZY=; b=/RqsmHqOrnkO2FAsERItdJNt5aGWeTughO42MhQRLWMQv9RlgKCwZJRbF5mcnHKQL2k+CH Czrcr+sAieaSLFAQ== From: Sebastian Andrzej Siewior To: Sergey Senozhatsky Cc: Andrew Morton , Yosry Ahmed , Hillf Danton , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 11/17] zsmalloc: make zspage lock preemptible Message-ID: <20250224085943.gChnQpEB@linutronix.de> References: <20250221222958.2225035-1-senozhatsky@chromium.org> <20250221222958.2225035-12-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250221222958.2225035-12-senozhatsky@chromium.org> X-Stat-Signature: bxetcxqnxu1wwsg81t3zokgbdoqwyxhs X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 86EE9C000D X-Rspam-User: X-HE-Tag: 1740387586-845479 X-HE-Meta: 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 0IPav/+I o+vDJRfmKwbIahBR+AE9xzYLDBfLSe5dR05ESq4vvFIm7OhFmaI/7za8lSJsUjyT3UsHLE5kegBFe9fNDcW74IRGKhg531UtrvNlRnIWPxRUHj/YOpUrPUGrnLk5FGuxgZ9V/8CKPUWVSvAnWvLfKqHwqJTF7F+fX8sH7v9BvKZuW0tt9eQGVMvZACoNtudYzY2CG 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 2025-02-22 07:25:42 [+0900], Sergey Senozhatsky wrote: > index 1424ee73cbb5..03710d71d022 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 No ifdef > }; > > static inline void zpdesc_set_first(struct zpdesc *zpdesc) > @@ -279,6 +294,93 @@ struct mapping_area { > enum zs_mapmode vm_mm; /* mapping mode */ > }; > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > +#define zsl_dep_map(zsl) (&(zsl)->dep_map) > +#define zspool_lock_class(pool) (&(pool)->lock_class) > +#else > +#define zsl_dep_map(zsl) NULL > +#define zspool_lock_class(pool) NULL > +#endif > + > +static void zspage_lock_init(struct zspage *zspage) > +{ > + struct zspage_lock *zsl = &zspage->zsl; > + > + lockdep_init_map(zsl_dep_map(zsl), "zspage->lock", > + zspool_lock_class(zspage->pool), 0); > + spin_lock_init(&zsl->lock); > + zsl->cnt = ZS_PAGE_UNLOCKED; > +} > + > +/* > + * The zspage lock can be held from atomic contexts, but it needs to remain > + * preemptible when held for reading because it remains held outside of those > + * atomic contexts, otherwise we unnecessarily lose preemptibility. > + * > + * To achieve this, the following rules are enforced on readers and writers: > + * > + * - Writers are blocked by both writers and readers, while readers are only > + * blocked by writers (i.e. normal rwlock semantics). > + * > + * - Writers are always atomic (to allow readers to spin waiting for them). > + * > + * - Writers always use trylock (as the lock may be held be sleeping readers). > + * > + * - Readers may spin on the lock (as they can only wait for atomic writers). > + * > + * - Readers may sleep while holding the lock (as writes only use trylock). > + */ > +static void zspage_read_lock(struct zspage *zspage) > +{ > + struct zspage_lock *zsl = &zspage->zsl; > + > + rwsem_acquire_read(zsl_dep_map(zsl), 0, 0, _RET_IP_); > + > + spin_lock(&zsl->lock); > + zsl->cnt++; > + spin_unlock(&zsl->lock); How is this working given that a read_lock always increments the counter? If it is write_locked then a read_lock makes it UNLOCKED. migrate_read_lock() did block if a writer was pending, this does not or at least it is not obvious how. > + lock_acquired(zsl_dep_map(zsl), _RET_IP_); > +} > + Sebastian