Conversation
osandov

Omar Sandoval

@vbabka I have a quick question that came up while I was adding a new drgn helper to count the number of allocated objects in a slab cache. Let me know if I should ask on the ML instead.

What is the purpose of the slab->frozen flag, and why do frozen slabs have slab->inuse == slab->objects?
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ptesarik@infosec.exchange

Petr Tesaล™รญk

Reply to @osandov

@osandov @vbabka FTR it will be greatly appreciated if you provide an actual answer rather than shit-posting as usual.
Cc: @ljs

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vbabka@mastodon.social

Vlastimil Babka ๐Ÿ‡จ๐Ÿ‡ฟ๐Ÿ‡ช๐Ÿ‡บ๐Ÿ‡บ๐Ÿ‡ฆ

Reply to @osandov
Edited 9 days ago

@osandov hi, frozen means some cpu has it installed as cpu slab for fastpath allocations so other cpus freeing objects to it must be more cautious and not move it to a node partial list etc. There will be inuse = objects before first such free because the freelist is detached when freezing and cpu has it on its kmem_cache_cpu. /proc/slabinfo doesn't count these cpu freelist so it's not precise. For more details these comments describe this and also cpu partial lists https://elixir.bootlin.com/linux/v6.16.4/source/mm/slub.c#L79

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vbabka@mastodon.social

Vlastimil Babka ๐Ÿ‡จ๐Ÿ‡ฟ๐Ÿ‡ช๐Ÿ‡บ๐Ÿ‡บ๐Ÿ‡ฆ

Reply to @ptesarik@infosec.exchange

@ptesarik @osandov @ljs hey Petr, had a bad morning or what? ;) when have I not answered such technical questions seriously before?

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ptesarik@infosec.exchange

Petr Tesaล™รญk

Reply to @vbabka@mastodon.social

@vbabka @osandov @ljs Had? Have!

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vbabka@mastodon.social

Vlastimil Babka ๐Ÿ‡จ๐Ÿ‡ฟ๐Ÿ‡ช๐Ÿ‡บ๐Ÿ‡บ๐Ÿ‡ฆ

Reply to @ptesarik@infosec.exchange

@ptesarik @osandov @ljs oh :( sorry to hear that.

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ptesarik@infosec.exchange

Petr Tesaล™รญk

Reply to @vbabka@mastodon.social

@vbabka @osandov @ljs Thanks, appreciated. It may get better if we engage in some shit-posting.

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vbabka@mastodon.social

Vlastimil Babka ๐Ÿ‡จ๐Ÿ‡ฟ๐Ÿ‡ช๐Ÿ‡บ๐Ÿ‡บ๐Ÿ‡ฆ

Reply to @ptesarik@infosec.exchange

@ptesarik @osandov @ljs also if you hail Satan!

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lkundrak@metalhead.club

AGRO TURBO.EXE SATAN ๐Ÿ‡บ๐Ÿ‡ฆ๐Ÿ‡จ๐Ÿ‡ฟ

Reply to @vbabka@mastodon.social

@vbabka @ptesarik @osandov @ljs ๐Ÿท

oh praise the morning star

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ptesarik@infosec.exchange

Petr Tesaล™รญk

Reply to @lkundrak@metalhead.club

@lkundrak @vbabka @osandov @ljs I have tried Praise of Death by Slayer, and it also worked.
Much better now.

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osandov

Omar Sandoval

Reply to @vbabka@mastodon.social
@vbabka thanks, that's super helpful! I'm embarrassed that I didn't see that comment. And that explains why /proc/slabinfo was giving me a different answer.
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