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 RF7tuplv 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From: Muchun Song > > The following diagram illustrates how to ensure the safety of the folio > lruvec lock when LRU folios undergo reparenting. > > In the folio_lruvec_lock(folio) function: > ``` > rcu_read_lock(); > retry: > lruvec = folio_lruvec(folio); > /* There is a possibility of folio reparenting at this point. */ > spin_lock(&lruvec->lru_lock); > if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) { > /* > * The wrong lruvec lock was acquired, and a retry is required. > * This is because the folio resides on the parent memcg lruvec > * list. > */ > spin_unlock(&lruvec->lru_lock); > goto retry; > } > > /* Reaching here indicates that folio_memcg() is stable. */ Does that mean we call rcu_read_unlock() in lruvec_unlock() instead of in folio_lruvec_lock() only to avoid false warnings inside the critical section, and technically calling rcu_read_unlock() right after acquiring the spinlock is fine? -- Cheers, Harry / Hyeonggon > ``` > > In the memcg_reparent_objcgs(memcg) function: > ``` > spin_lock(&lruvec->lru_lock); > spin_lock(&lruvec_parent->lru_lock); > /* Transfer folios from the lruvec list to the parent's. */ > spin_unlock(&lruvec_parent->lru_lock); > spin_unlock(&lruvec->lru_lock); > ``` > > After acquiring the lruvec lock, it is necessary to verify whether > the folio has been reparented. If reparenting has occurred, the new > lruvec lock must be reacquired. During the LRU folio reparenting > process, the lruvec lock will also be acquired (this will be > implemented in a subsequent patch). Therefore, folio_memcg() remains > unchanged while the lruvec lock is held. > > Given that lruvec_memcg(lruvec) is always equal to folio_memcg(folio) > after the lruvec lock is acquired, the lruvec_memcg_debug() check is > redundant. Hence, it is removed. > > This patch serves as a preparation for the reparenting of LRU folios. > > Signed-off-by: Muchun Song > Signed-off-by: Qi Zheng > ---