From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="q8/JA6e8" Received: from mail-lj1-x229.google.com (mail-lj1-x229.google.com [IPv6:2a00:1450:4864:20::229]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9F7D1BD for ; Tue, 5 Dec 2023 22:00:32 -0800 (PST) Received: by mail-lj1-x229.google.com with SMTP id 38308e7fff4ca-2ca0c36f5beso34416881fa.1 for ; Tue, 05 Dec 2023 22:00:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1701842430; x=1702447230; darn=vger.kernel.org; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=pYq7dca+Gj7nooc7F/6CDn/Z/YkbYvbbjyp+G0CHbFs=; b=q8/JA6e8J2GfDlvAF0MP1P3w481K0P2Nf6S4PQcV1k/ioS66LU7FHv/2dz5JR4RcwI Hl3x81fUSCcn4zvWZhgq6kGkJjjwJcY5O14EEUQaorbU59hk9iPaD7DRt1Ot3SwPz4/2 HCGbIhB8I+ka/a8MPpYVYmhIhxy5stP5II+KIRPZcQdU89anGB7fd/dVfIXPNqZp1xD0 5xZn5m4C7VMoZ0A8+oU3M2eD2rUNjKVSkOyvFTC77HslFPp7uLfwmguTbulF+KsXhnS1 yqtEFl4fOaoA5Xd8Zz5Vb9HZf1niS0gkqbtWJeIlzt8W5DWR96R/7bijY2TICAk5kaRH 19ZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701842430; x=1702447230; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=pYq7dca+Gj7nooc7F/6CDn/Z/YkbYvbbjyp+G0CHbFs=; b=FD0GT17TfbI1r3/N9Nh/Jk0yYXZLOlEIpD93CRa4HGLZ6/IWPbiYKX7TOxuS9zYZKZ b40v0OTkqkU4bikP0AdEdvPubvdYsUuGbuZp7oVTwOcCMcVfuwiAhkIiFfxiW2bVIJqX VO444+muIbaFgPjg7bL/vaIFqmSY+70CFBlcq2aXVD56ya19aiDAtVMAqzak4E866bJk kjHXZX18XK/j2lrhMJEE6h2AXALLovYiUKLHIwk9Q/vkm2mfySN6my2GcSpVsSk9OwGf HHbKQdl8hSEIFT0SdINNtDM77SaKFoipEd/eYU9s8IJpeGFTUsPmGyoEthxIcAvSWdqM 6Rbw== X-Gm-Message-State: AOJu0YyHKNlpa9Gy3WKH/B6pM/4E8jSi3hCzQccQm3iWxp+FOQMfhynO ryI1EpqRdM689k2LWhY3aXsY/fS3/sUTYAA0trmpBg== X-Google-Smtp-Source: AGHT+IFXAeoJL6ZSpivoVRoRx5sclW/hkOTwH9MNxBDf0+k3EyWFJczCRuAq+UUItgKlQjTWq1Kko/YxHxXsgyIZ2LI= X-Received: by 2002:a2e:87d7:0:b0:2ca:ac6:9f94 with SMTP id v23-20020a2e87d7000000b002ca0ac69f94mr178430ljj.86.1701842430004; Tue, 05 Dec 2023 22:00:30 -0800 (PST) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20231130194023.4102148-1-nphamcs@gmail.com> <20231130194023.4102148-7-nphamcs@gmail.com> In-Reply-To: From: Yosry Ahmed Date: Tue, 5 Dec 2023 21:59:50 -0800 Message-ID: Subject: Re: [PATCH v8 6/6] zswap: shrinks zswap pool based on memory pressure To: Chengming Zhou Cc: Nhat Pham , 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" [..] > > @@ -526,6 +582,102 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root, > > return entry; > > } > > > > +/********************************* > > +* shrinker functions > > +**********************************/ > > +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l, > > + spinlock_t *lock, void *arg); > > + > > +static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, > > + struct shrink_control *sc) > > +{ > > + struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid)); > > + unsigned long shrink_ret, nr_protected, lru_size; > > + struct zswap_pool *pool = shrinker->private_data; > > + bool encountered_page_in_swapcache = false; > > + > > + nr_protected = > > + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); > > + lru_size = list_lru_shrink_count(&pool->list_lru, sc); > > + > > + /* > > + * Abort if the shrinker is disabled or if we are shrinking into the > > + * protected region. > > + * > > + * This short-circuiting is necessary because if we have too many multiple > > + * concurrent reclaimers getting the freeable zswap object counts at the > > + * same time (before any of them made reasonable progress), the total > > + * number of reclaimed objects might be more than the number of unprotected > > + * objects (i.e the reclaimers will reclaim into the protected area of the > > + * zswap LRU). > > + */ > > + if (!zswap_shrinker_enabled || nr_protected >= lru_size - sc->nr_to_scan) { > > + sc->nr_scanned = 0; > > + return SHRINK_STOP; > > + } > > + > > + shrink_ret = list_lru_shrink_walk(&pool->list_lru, sc, &shrink_memcg_cb, > > + &encountered_page_in_swapcache); > > + > > + if (encountered_page_in_swapcache) > > + return SHRINK_STOP; > > + > > + return shrink_ret ? shrink_ret : SHRINK_STOP; > > +} > > + > > +static unsigned long zswap_shrinker_count(struct shrinker *shrinker, > > + struct shrink_control *sc) > > +{ > > + struct zswap_pool *pool = shrinker->private_data; > > + struct mem_cgroup *memcg = sc->memcg; > > + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid)); > > + unsigned long nr_backing, nr_stored, nr_freeable, nr_protected; > > + > > +#ifdef CONFIG_MEMCG_KMEM > > + cgroup_rstat_flush(memcg->css.cgroup); > > + nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT; > > + nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); > > +#else > > + /* use pool stats instead of memcg stats */ > > + nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT; > > + nr_stored = atomic_read(&pool->nr_stored); > > +#endif > > + > > + if (!zswap_shrinker_enabled || !nr_stored) > When I tested with this series, with !zswap_shrinker_enabled in the default case, > I found the performance is much worse than that without this patch. > > Testcase: memory.max=2G, zswap enabled, kernel build -j32 in a tmpfs directory. > > The reason seems the above cgroup_rstat_flush(), caused much rstat lock contention > to the zswap_store() path. And if I put the "zswap_shrinker_enabled" check above > the cgroup_rstat_flush(), the performance become much better. > > Maybe we can put the "zswap_shrinker_enabled" check above cgroup_rstat_flush()? Yes, we should do nothing if !zswap_shrinker_enabled. We should also use mem_cgroup_flush_stats() here like other places unless accuracy is crucial, which I doubt given that reclaim uses mem_cgroup_flush_stats(). mem_cgroup_flush_stats() has some thresholding to make sure we don't do flushes unnecessarily, and I have a pending series in mm-unstable that makes that thresholding per-memcg. Keep in mind that adding a call to mem_cgroup_flush_stats() will cause a conflict in mm-unstable, because the series there adds a memcg argument to mem_cgroup_flush_stats(). That should be easily amenable though, I can post a fixlet for my series to add the memcg argument there on top of users if needed. > > Thanks! > > > + return 0; > > + > > + nr_protected = > > + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); > > + nr_freeable = list_lru_shrink_count(&pool->list_lru, sc); > > + /* > > + * Subtract the lru size by an estimate of the number of pages > > + * that should be protected. > > + */ > > + nr_freeable = nr_freeable > nr_protected ? nr_freeable - nr_protected : 0; > > + > > + /* > > + * Scale the number of freeable pages by the memory saving factor. > > + * This ensures that the better zswap compresses memory, the fewer > > + * pages we will evict to swap (as it will otherwise incur IO for > > + * relatively small memory saving). > > + */ > > + return mult_frac(nr_freeable, nr_backing, nr_stored); > > +} > > + > > +static void zswap_alloc_shrinker(struct zswap_pool *pool) > > +{ > > + pool->shrinker = > > + shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap"); > > + if (!pool->shrinker) > > + return; > > + > > + pool->shrinker->private_data = pool; > > + pool->shrinker->scan_objects = zswap_shrinker_scan; > > + pool->shrinker->count_objects = zswap_shrinker_count; > > + pool->shrinker->batch = 0; > > + pool->shrinker->seeks = DEFAULT_SEEKS; > > +} > > + > > /********************************* > > * per-cpu code > > **********************************/ [..]