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Date: Thu, 26 May 2016 15:21:54 -0400 From: Tejun Heo <tj@...nel.org> To: Vlastimil Babka <vbabka@...e.cz> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Sasha Levin <sasha.levin@...cle.com>, Alexei Starovoitov <ast@...nel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Christoph Lameter <cl@...ux.com>, Linux-MM layout <linux-mm@...ck.org>, Marco Grassi <marco.gra@...il.com> Subject: Re: [PATCH percpu/for-4.7-fixes 1/2] percpu: fix synchronization between chunk->map_extend_work and chunk destruction Hello, On Thu, May 26, 2016 at 11:19:06AM +0200, Vlastimil Babka wrote: > > if (is_atomic) { > > margin = 3; > > > > if (chunk->map_alloc < > > - chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW && > > - pcpu_async_enabled) > > - schedule_work(&chunk->map_extend_work); > > + chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) { > > + if (list_empty(&chunk->map_extend_list)) { > So why this list_empty condition? Doesn't it deserve a comment then? And Because doing list_add() twice corrupts the list. I'm not sure that deserves a comment. We can do list_move() instead but that isn't necessarily better. > isn't using a list an overkill in that case? That would require rebalance work to scan all chunks whenever it's scheduled and if a lot of atomic allocations are taking place, it has some possibility to become expensive with a lot of chunks. Thanks. -- tejun
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