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Fri, 20 Mar 2026 09:18:47 -0700 (PDT) Date: Fri, 20 Mar 2026 12:18:43 -0400 From: Johannes Weiner To: Shakeel Butt Cc: Andrew Morton , David Hildenbrand , Yosry Ahmed , Zi Yan , "Liam R. Howlett" , Usama Arif , Kiryl Shutsemau , Dave Chinner , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 5/7] mm: list_lru: introduce caller locking for additions and deletions Message-ID: References: <20260318200352.1039011-1-hannes@cmpxchg.org> <20260318200352.1039011-6-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: F1860C000D X-Stat-Signature: j4zg5h85o51ttj171pycrp4ho9m711q4 X-Rspam-User: X-HE-Tag: 1774023528-712346 X-HE-Meta: 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 4rt0EMI2 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 18, 2026 at 01:51:04PM -0700, Shakeel Butt wrote: > On Wed, Mar 18, 2026 at 03:53:23PM -0400, Johannes Weiner wrote: > > Locking is currently internal to the list_lru API. However, a caller > > might want to keep auxiliary state synchronized with the LRU state. > > > > For example, the THP shrinker uses the lock of its custom LRU to keep > > PG_partially_mapped and vmstats consistent. > > > > To allow the THP shrinker to switch to list_lru, provide normal and > > irqsafe locking primitives as well as caller-locked variants of the > > addition and deletion functions. > > > > Reviewed-by: David Hildenbrand (Arm) > > Signed-off-by: Johannes Weiner > > One nit below, other than that: > > Acked-by: Shakeel Butt > > > > > -static inline void lock_list_lru(struct list_lru_one *l, bool irq) > > +static inline void lock_list_lru(struct list_lru_one *l, bool irq, > > + unsigned long *irq_flags) > > { > > - if (irq) > > + if (irq_flags) > > + spin_lock_irqsave(&l->lock, *irq_flags); > > + else if (irq) > > If we move __list_lru_walk_one to use irq_flags then we can remove the irq > param. It is reclaim code path and I don't think additional cost of irqsave > would matter here. The workingset shrinker's isolation function uses unlock_irq() and cond_resched(). That would be non-trivial to rewrite - pass flags around; keep irqs disabled for the whole reclaim cycle; break it into a two-stage process. This sounds like a higher maintenance burden than the bool here. I know there is some cost to this distinction, but I actually do find it useful to know the difference. It's self-documenting context.