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Date: Thu, 23 Sep 2021 06:28:44 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Jens Axboe <axboe@...nel.dk> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>, John Garry <john.garry@...wei.com>, linux-block@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [RFC v2 PATCH] mm, sl[au]b: Introduce lockless cache On Wed, 22 Sep 2021 06:58:00 -0600 Jens Axboe wrote: > > I considered only case 2) when writing code. Well, To support 1), > > I think there are two ways: > > > > a) internally call kmem_cache_free when in_interrupt() is true > > b) caller must disable interrupt when freeing > > > > I think a) is okay, how do you think? > > If the API doesn't support freeing from interrupts, then I'd make that > the rule. Caller should know better if that can happen, and then just > use kmem_cache_free() if in a problematic context. That avoids polluting > the fast path with that check. I'd still make it a WARN_ON_ONCE() as > described and it can get removed later, hopefully. Shooting from the hip a little but if I'm getting the context right this is all very similar to the skb cache so lockdep_assert_in_softirq() may be useful: /* * Acceptable for protecting per-CPU resources accessed from BH. * Much like in_softirq() - semantics are ambiguous, use carefully. */ #define lockdep_assert_in_softirq() \ do { \ WARN_ON_ONCE(__lockdep_enabled && \ (!in_softirq() || in_irq() || in_nmi())); \ } while (0)
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