On Sat, Aug 14, 2021 at 01:25:10PM +0800, Muchun Song wrote: > The diagram below shows how to make the folio lruvec lock safe when LRU > pages are reparented. > > folio_lruvec_lock(folio) > retry: > lruvec = folio_lruvec(folio); > > // The folio is reparented at this time. > spin_lock(&lruvec->lru_lock); > > if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) > // Acquired the wrong lruvec lock and need to retry. > // Because this folio is on the parent memcg lruvec list. > goto retry; > > // If we reach here, it means that folio_memcg(folio) is stable. > > memcg_reparent_objcgs(memcg) > // lruvec belongs to memcg and lruvec_parent belongs to parent memcg. > spin_lock(&lruvec->lru_lock); > spin_lock(&lruvec_parent->lru_lock); > > // Move all the pages from the lruvec list to the parent lruvec list. > > spin_unlock(&lruvec_parent->lru_lock); > spin_unlock(&lruvec->lru_lock); > > After we acquire the lruvec lock, we need to check whether the folio is > reparented. If so, we need to reacquire the new lruvec lock. On the > routine of the LRU pages reparenting, we will also acquire the lruvec > lock (will be implemented in the later patch). So folio_memcg() cannot > be changed when we hold the lruvec lock. > > Since lruvec_memcg(lruvec) is always equal to folio_memcg(folio) after > we hold the lruvec lock, lruvec_memcg_debug() check is pointless. So > remove it. > > This is a preparation for reparenting the LRU pages. > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> > Acked-by: Roman Gushchin <guro@xxxxxx> Maybe it's mostly s/page/folio, but the patch looks quite differently in comparison to the version I did ack. In general, please, drop acks when there are significant changes between versions. Thanks!
