shrink_slab(9)

💅 shrink_slab — bestie edition

ok so this is a page from the Kernel API Manual, and we're talking about shrink_slab — a lil kernel function with main character energy that shrinks slab caches. yes. that's the whole vibe. let's get into it 🎀

✨ NAME ✨

shrink_slab — shrink slab caches. that's it. that's the function. it makes the slab caches smaller and honestly it ate 💅

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🌸 SYNOPSIS 🌸

unsigned long shrink_slab (gfp_t gfp_mask , int nid , struct mem_cgroup
*memcg , int priority );

look at her. four arguments, returns an unsigned long. iconic behavior fr fr ✨

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🦋 ARGUMENTS 🦋

• gfp_mask — the allocation context. yep, that's the whole description, it's giving minimal and mysterious 🙈
• nid — the node whose slab caches we're targeting. very "I know a guy" energy.
• memcg — the memory cgroup whose slab caches we're targeting. sister argument to nid, we love a matched set 💖
• priority — the reclaim priority. lowkey the moment of truth, more on that below 👑

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🔥 DESCRIPTION 🔥

So what does she actually do? She calls the shrink functions to age shrinkable caches. that's the job. that's the assignment. aging caches like they're fine wine 🍓

Now the details, bestie, don't skip:

nid gets passed along to shrinkers that have SHRINKER_NUMA_AWARE set. the unaware shrinkers — bless them — will receive a node id of 0 instead. no cap, that's literally just how it works.

memcg specifies the memory cgroup to target. and here's the thing: the unaware shrinkers are called only if it is the root cgroup. so if you're not at root, those unaware shrinkers are simply not invited to the function. sorry bestie 🫶

priority is sc->priority — and this part is so clever. we take the number of objects and >> by priority in order to get the scan target. shift it right, that's the whole trick. the way that priority just slides the numbers down 😭✨

and the return value? the number of reclaimed slab objects. that's your receipt. keep it.

⚠️ tiny heads-up: everything above is exactly what the page says — I'm not adding lore, that's all of it 💀

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👑 SEE ALSO 👑

• Kernel file ./mm/shrinker.c — go read the source, bestie, it's right there 🔥

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ok that's the whole page and honestly it was short but she made her point 🌈 stay shiny, keep your caches aged, and remember: unaware shrinkers get node id 0 and they get called only at the root cgroup. periodt. 💜

— this has been the ./mm corner of the world, dated October 2026, brought to you by the shrink_slab(9) entry itself 🎀✨