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Fri, 23 Feb 2024 09:17:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id JVgDO65i2GUiRAAAD6G6ig (envelope-from ); Fri, 23 Feb 2024 09:17:34 +0000 Message-ID: <4a8aa758-175e-471c-9c22-bb61dbb956e8@suse.cz> Date: Fri, 23 Feb 2024 10:17:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] slub: avoid scanning all partial slabs in get_slabinfo() Content-Language: en-US To: Jianfeng Wang , "Christoph Lameter (Ampere)" , Chengming Zhou Cc: David Rientjes , penberg@kernel.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chengming Zhou References: <20240215211457.32172-1-jianfeng.w.wang@oracle.com> <6b58d81f-8e8f-3732-a5d4-40eece75013b@google.com> <55ccc92a-79fa-42d2-97d8-b514cf00823b@linux.dev> <6daf88a2-84c2-5ba4-853c-c38cca4a03cb@linux.com> <93497e03-1acf-483e-8695-e103fd1bc044@oracle.com> From: Vlastimil Babka In-Reply-To: <93497e03-1acf-483e-8695-e103fd1bc044@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3B90014000A X-Stat-Signature: oa5m73ajpfafcmueuheasw447d9wun3y X-HE-Tag: 1708679857-385793 X-HE-Meta: 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 R57pIwrb PlKhVfGJj4UqY2oFIBE4WRi+hafA1IUvvTXaHb1R8wsebzvYn5kcpUZ52x+mIYy9uMbBA/NibkLVM3LZXsMwXWZBB3qKZTC5rf/+1iWydKPIcsqCwf/YgCz1WLUEh24ingHq0I/h4sHfnG5Xu+SrAlGnRORoGFR70bFf8GD6SUTQeR5FgXhZYjWc+KHyYv1uqAQK8WDEWi+68K5Q5ig2wbbPGoF/xaKMvSjzrmgt2759wjOQh9DpWM3rAaHmKF/830JUOf9cYptccIXCHdvA4pyDvnk8eB0XAYreVk9gMKq1fw9/i4mGkVHgygK4EOV9eXPTn6ZKgyTj0mc37L7jZ/pAYkFJJmmg0SVPolz/CxDL6Xo4BaxRBVddJUxF1khf4wPPT X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 2/23/24 08:36, Jianfeng Wang wrote: > > On 2/22/24 7:02 PM, Christoph Lameter (Ampere) wrote: >> On Thu, 22 Feb 2024, Chengming Zhou wrote: >> >>> Anyway, I put the code below for discussion... >> >> Can we guestimate the free objects based on the number of partial slabs. That number is available. >> > > Yes. > I've thought about calculating the average number of free objects in a > partial slab (through sampling) and then estimating the total number of > free objects as (avg * n->nr_partial). > > See the following. > > --- > mm/slub.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 63d281dfacdb..13385761049c 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2963,6 +2963,8 @@ static inline bool free_debug_processing(struct kmem_cache *s, > #endif /* CONFIG_SLUB_DEBUG */ > > #if defined(CONFIG_SLUB_DEBUG) || defined(SLAB_SUPPORTS_SYSFS) > +#define MAX_PARTIAL_TO_SCAN 10000 > + > static unsigned long count_partial(struct kmem_cache_node *n, > int (*get_count)(struct slab *)) > { > @@ -2971,8 +2973,22 @@ static unsigned long count_partial(struct kmem_cache_node *n, > struct slab *slab; > > spin_lock_irqsave(&n->list_lock, flags); > - list_for_each_entry(slab, &n->partial, slab_list) > - x += get_count(slab); > + if (n->nr_partial > MAX_PARTIAL_TO_SCAN) { > + /* Estimate total count of objects via sampling */ > + unsigned long sample_rate = n->nr_partial / MAX_PARTIAL_TO_SCAN; > + unsigned long scanned = 0; > + unsigned long counted = 0; > + list_for_each_entry(slab, &n->partial, slab_list) { Unfortunately this is still going through the whole list. > + if (++scanned % sample_rate == 0) { > + x += get_count(slab); The get_count() itself is trivial, so this won't help much. (except saving a function call which can be noticeable with all the retpolines and other unfortunate stuff these days; we could refactor the code to be inline, but processing the whole long list would still be an issue). So this would have to instead count first up to MAX_PARTIAL_TO_SCAN slabs and then terminate the loop. This can make the sampling biased, unfortunately. > + counted++; > + } > + } > + x = mult_frac(x, n->nr_partial, counted); > + } else { > + list_for_each_entry(slab, &n->partial, slab_list) > + x += get_count(slab); > + } > spin_unlock_irqrestore(&n->list_lock, flags); > return x; > }