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List:       linux-kernel
Subject:    Re: [GIT PULL] slab updates for 6.10
From:       Linus Torvalds <torvalds () linux-foundation ! org>
Date:       2024-05-13 17:33:46
Message-ID: CAHk-=wiZpyWvC-nh4CPhKkPLMwWb_W00NDMopuxVNTnGB7fYeg () mail ! gmail ! com
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On Thu, 9 May 2024 at 07:25, Vlastimil Babka <vbabka@suse.cz> wrote:
>
>   To avoid affecting fast paths with another shared counter (attempted in the
>   past) or complex partial list traversal schemes that allow rescheduling, the
>   chosen solution resorts to approximation - when the partial list is over
>   10000 slabs long, we will only traverse first 5000 slabs from head and tail
>   each and use the average of those to estimate the whole list. Both head and
>   tail are used as the slabs near head to tend to have more free objects than
>   the slabs towards the tail.

I suspect you could have cut this down by an order of magnitude, and
made the limit be just 1k slabs rather than 10k slabs. Or even
_another_ order of magnitude smaller.

Somebody was being a bit too worried about approximations, methinks -
but I think the real worry goes the other way, where it's practically
so hard to even hit the approximation situation that it gets no
testing at all.

IOW, I suspect it's better to be explicit about approximations, and
have people aware of it, rather than be overly cautious and have it be
a special case that almost never triggers in any normal loads.

But pulled.

              Linus

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