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Mon, 06 Nov 2023 15:25:16 -0800 (PST) MIME-Version: 1.0 References: <20231106183159.3562879-1-nphamcs@gmail.com> <20231106183159.3562879-4-nphamcs@gmail.com> In-Reply-To: From: Nhat Pham Date: Mon, 6 Nov 2023 15:25:05 -0800 Message-ID: Subject: Re: [PATCH v5 3/6] zswap: make shrinking memcg-aware To: Yosry Ahmed Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, cerasuolodomenico@gmail.com, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, chrisl@kernel.org, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, shuah@kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E3D8DC001A X-Stat-Signature: zyo9g4x6cj1qre5jobijuqfsgmoot457 X-Rspam-User: X-HE-Tag: 1699313116-350911 X-HE-Meta: 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 wQROIxYX OGpo4DWZ9iY/oBGvfXUaS+820A3jXp3JPqjItQkjmozfK2WxOFlP2QHag/hCJHVMVwz/2BuLU9zINUfWUd8S+CkIyaKN/RoNMzQiXpO+85wm/57U40xSyzB9AOeEZqruqrssC0P0lWmkFKV8Q7ba3oFIIe2O0O16ibh6y1p5xOvq2DmCNGGdnmuC2Ew3arPenSpSW6PMzR9YHa03s9iEAziIvJ3Xvrt8IK0tDPHQZEadcvkGM4LHp4ycod1KOn3ecqMGvydeZryY2l4df3Ip0TE6WtMiknS/lJSlh X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 Mon, Nov 6, 2023 at 12:58=E2=80=AFPM Yosry Ahmed = wrote: > > > > > > > This lock is only needed to synchronize updating pool->next_shrink, > > > right? Can we just use atomic operations instead? (e.g. cmpxchg()). > > > > I'm not entirely sure. I think in the pool destroy path, we have to als= o > > put the next_shrink memcg, so there's that. > > We can use xchg() to replace it with NULL, then put the memcg ref, no? > > We can also just hold zswap_pools_lock while shrinking the memcg > perhaps? It's not a contended lock anyway. It just feels weird to add > a spinlock to protect one pointer. Ah this sounds good to me I guess. I'm not opposed to this simplification of the concurrency scheme. > > > > > > > > > > + if (pool->next_shrink =3D=3D memcg) > > > > + pool->next_shrink =3D > > > > + mem_cgroup_iter(NULL, pool->next_sh= rink, NULL, true); > > > > + spin_unlock(&pool->next_shrink_lock); > > > > + } > > > > + spin_unlock(&zswap_pools_lock); > > > > +} > > > > + > > > > /********************************* > > > > * zswap entry functions > > > > **********************************/ > > > > static struct kmem_cache *zswap_entry_cache; > > > > > > > > -static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) > > > > +static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int = nid) > > > > { > > > > struct zswap_entry *entry; > > > > - entry =3D kmem_cache_alloc(zswap_entry_cache, gfp); > > > > + entry =3D kmem_cache_alloc_node(zswap_entry_cache, gfp, nid= ); > > > > if (!entry) > > > > return NULL; > > > > entry->refcount =3D 1; > > > [..] > > > > @@ -1233,15 +1369,15 @@ bool zswap_store(struct folio *folio) > > > > zswap_invalidate_entry(tree, dupentry); > > > > } > > > > spin_unlock(&tree->lock); > > > > - > > > > - /* > > > > - * XXX: zswap reclaim does not work with cgroups yet. Witho= ut a > > > > - * cgroup-aware entry LRU, we will push out entries system-= wide based on > > > > - * local cgroup limits. > > > > - */ > > > > objcg =3D get_obj_cgroup_from_folio(folio); > > > > - if (objcg && !obj_cgroup_may_zswap(objcg)) > > > > - goto reject; > > > > + if (objcg && !obj_cgroup_may_zswap(objcg)) { > > > > + memcg =3D get_mem_cgroup_from_objcg(objcg); > > > > + if (shrink_memcg(memcg)) { > > > > + mem_cgroup_put(memcg); > > > > + goto reject; > > > > + } > > > > + mem_cgroup_put(memcg); > > > > > > Can we just use RCU here as well? (same around memcg_list_lru_alloc() > > > call below). > > > > For memcg_list_lru_alloc(): there's potentially sleeping in that piece = of > > code I believe? I believe at the very least we'll have to use this gfp_= t > > flag for it to be rcu-safe: > > > > GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN > > not sure the > > > > Same go for this particular place IIRC - there's some sleeping done > > in zswap_writeback_entry(), correct? > > Ah right, I missed this. My bad.