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U2FsdGVkX18flBLkjNta46z4/bJpo3uBl/FxpBgtLaCURxKq/KbJBjQM/4dPLoSHEglAInw9QlHnTECoruz5Hj11XUO8W9jMrGEhrUtdIKZYICcqmE7DH/idRTm1ICyooxEYq2DojD5lx3YRCD2PRq8ZgVid+E6dQV93k94T4pQcUfiJOecdOhQznGqKyiDkqW7YTO9LORdM1Z1YKQOUoytBsedzui71cz7cSHH8q6qVeFRs3OOHgY5V9YAizeRoZK7XiRC+JjFXxWxgsqDHoIL4aiupJFA/zQvs5HNQDjHWYkmzOG5UGU4vcK3hPdicg7p/3Z5Bb6AbcAdAm84WBdyxKbNf1oS2bQvqbTEN94W5u+o1JFhgapERztPzm4JlItZLGHiJQTzjWFZAic7K3HPMvFnJHisyJRFjtlDeIp8J2fKLt6Z91kZCsiC7SZsgS5Ci+JeCs82JazmcEhGOOs/NzhJ7aKjZRwL2uSl/M4Bbvxa65YzHxTnyC35GIm6OifiuPIR1vzmZ97o/sFpM2gq/x9K6neGm4JEfHK4niUsMfBRAHW18xRWrU7QoDjNcUpA4pujbuNosqTi/1jMlEjtoyHf1Kb2K1QXVk6QWBxuC45+ePo1dhLrUHVLYrpGiMvJ5fsItjHAoXLDkfXs2vAI3Fm+wTDxxcoT5aufiFncoexdBhAfjRt0uG8X1HUp2sX5DTnomV3gwj0B1YxYaB1JWQNmOrDacmVIpzOlH0C1YU8aIfmFtF2rMrGeLNR2wH3vdm52SpUysLh58KPzlvV4w9tu0ZThpKOqnoNvZ7jxPI8NIP7X6G9gfDEU+7EPB3SpEK4JOf7p387z5sOCndYqmMebyHwk1GydAmSEEBX9h4DjgIF0mxDPbLAT8EH1xuVb2W0rt03myDGQwnTcTg/ruLhKkIrVeba88FppmdSvuJe7Jwf3DJmQc7YvEwwH4ld/uqOM+St7nghyE5ZI /B0EtYmA 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 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 2/22/24 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) { + if (++scanned % sample_rate == 0) { + x += get_count(slab); + 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; } -- > How accurate need the accounting be? We also have fuzzy accounting in the VM counters. Based on my experience, for a |kmem_cache|, the total number of objects can tell whether the |kmem_cache| has been heavily used by a workload. When the total number is large: if the number of free objects is small, then either these objects are really in-use or there is *memory leak* going on (which then must be further diagnosed). However, if the number of free objects is large, we can only know the slab memory fragmentation happens. So, I think the object accounting needn't be accurate. We only have to tell whether a large percentage of slab objects is free or not. The above code is a sampling, which should do the job if we take enough samples.