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Date: Thu, 26 May 2016 22:48:54 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: Tejun Heo <tj@...nel.org> 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 On 26.5.2016 21:21, Tejun Heo wrote: > 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. Ugh, right, somehow I thought it was testing &pcpu_map_extend_chunks. My second question was based on the assumption that the list can have only one item. Sorry about the noise. >> 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. >
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