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Howlett" , Vlastimil Babka , Yu Zhao , Zi Yan , Qi Zheng , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Kairui Song References: <20260818-mglru-flags-cleanup-v1-0-8dbbdac0d28c@tencent.com> <20260818-mglru-flags-cleanup-v1-1-8dbbdac0d28c@tencent.com> From: Ridong Chen In-Reply-To: <20260818-mglru-flags-cleanup-v1-1-8dbbdac0d28c@tencent.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6A40980002 X-Stat-Signature: s67wq6fgm9a44yrid685r1n9ndffi8kz X-Rspam-User: X-HE-Tag: 1787105125-949976 X-HE-Meta: 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 Nfm1L1DP WBDJf3d9B7cUkcQgvLk+mN3Ojnn+IomCU3X3DpirpXlN0Q5ap91PzKbUQSY9rc+qoQLZx6OhmbdLfSv4mujEKVNMKNVp8Y3WJPXhY9buFufwUYOY2c2Qn53gdnBvsO60RbC40SOHdy9N5thNl1dquM6aYn1aP52Vktlzd2/8f0nSqUv2tM0UbUMY0I6RzbAExBv7widAnjj/UDZLLw247fvWd/fy2Oo+xYLj2OnyqMURUrAlCv0pNZW/YsTlejy4ThUMm9UJ4aM3nkPH11db/RbOMY2yTUfQqe35MMkUI+IOsR6GT8QIXCw/EoFm/wTbw2muNv/PrK85akjtwSjkkzgMrbXwRaZzhWkMA Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/18/2026 1:38 PM, Kairui Song via B4 Relay wrote: > From: Kairui Song > > commit ca707239e8a7 ("mm: update_lru_size warn and reset bad lru_size") > introduced a sanity check to catch memcg counter underflow, which was > more of a workaround for another bug: lru_zone_size is unsigned, so > underflow wraps it around and returns an enormously large number, then > the memcg shrinker loops almost forever as the calculated number of > folios to shrink is huge. That commit also checked if a zero value > matches the empty LRU list, so we have to hold the LRU lock, and > handle the positive and negative deltas separately. > > But later commit b4536f0c829c ("mm, memcg: fix the active list aging > for lowmem requests when memcg is enabled") already removed the LRU > emptiness check, so handling the deltas separately is no longer > needed. And if we just turn it into an atomic long, underflow isn't a > big issue either, and can be checked at the reader side, which is > called much less frequently than the updater. > > So let's turn the counter into an atomic long and check at the reader > side instead, which has a smaller overhead. The underflow correction > is removed: a massive leak of the LRU size counter would indicate > that something else has gone very wrong, and one should fix that > leaking site instead. Besides, the updater-side sanity check is > unlikely to catch the leaking site anyway: if a folio was removed > without updating the counter while other folios remain on the LRU, > the WARN only triggers much later, from a likely innocent callsite. > > Signed-off-by: Kairui Song > --- > include/linux/memcontrol.h | 9 +++++++-- > mm/memcontrol.c | 18 +----------------- > 2 files changed, 8 insertions(+), 19 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index e78bc98ab229..b13e3f056319 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -113,7 +113,7 @@ struct mem_cgroup_per_node { > /* Fields which get updated often at the end. */ > struct lruvec lruvec; > CACHELINE_PADDING(_pad2_); > - unsigned long lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS]; > + atomic_long_t lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS]; > struct mem_cgroup_reclaim_iter iter; > > /* > @@ -897,10 +897,15 @@ static inline > unsigned long mem_cgroup_get_zone_lru_size(struct lruvec *lruvec, > enum lru_list lru, int zone_idx) > { > + long val; > struct mem_cgroup_per_node *mz; > > mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec); > - return READ_ONCE(mz->lru_zone_size[zone_idx][lru]); > + val = atomic_long_read(&mz->lru_zone_size[zone_idx][lru]); > + if (WARN_ON_ONCE(val < 0)) > + return 0; > + > + return val; > } > > void __mem_cgroup_handle_over_high(gfp_t gfp_mask); > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1d3339520809..9d0ee3d3bda7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1529,28 +1529,12 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru, > int zid, long nr_pages) > { > struct mem_cgroup_per_node *mz; > - unsigned long *lru_size; > - long size; > > if (mem_cgroup_disabled()) > return; > > mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec); > - lru_size = &mz->lru_zone_size[zid][lru]; > - > - if (nr_pages < 0) > - *lru_size += nr_pages; > - > - size = *lru_size; > - if (WARN_ONCE(size < 0, > - "%s(%p, %d, %ld): lru_size %ld\n", > - __func__, lruvec, lru, nr_pages, size)) { > - VM_BUG_ON(1); > - *lru_size = 0; > - } > - This code is confusing, I used to try to remove it. Well done. > - if (nr_pages > 0) > - *lru_size += nr_pages; > + atomic_long_add(nr_pages, &mz->lru_zone_size[zid][lru]); > } > > /** > Looks good to me. Reviewed-by: Ridong Chen -- Best regards Ridong