> -----Original Message----- > From: Dennis Zhou [mailto:dennis@xxxxxxxxxx] > Sent: 2019年3月3日 6:32 > To: Peng Fan <peng.fan@xxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx>; Christoph Lameter <cl@xxxxxxxxx>; Vlad > Buslov <vladbu@xxxxxxxxxxxx>; kernel-team@xxxxxx; linux-mm@xxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 04/12] percpu: manage chunks based on contig_bits > instead of free_bytes > > On Sat, Mar 02, 2019 at 01:48:20PM +0000, Peng Fan wrote: > > > > > > > -----Original Message----- > > > From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] > On > > > Behalf Of Dennis Zhou > > > Sent: 2019年2月28日 10:19 > > > To: Dennis Zhou <dennis@xxxxxxxxxx>; Tejun Heo <tj@xxxxxxxxxx>; > > > Christoph Lameter <cl@xxxxxxxxx> > > > Cc: Vlad Buslov <vladbu@xxxxxxxxxxxx>; kernel-team@xxxxxx; > > > linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > > Subject: [PATCH 04/12] percpu: manage chunks based on contig_bits > > > instead of free_bytes > > > > > > When a chunk becomes fragmented, it can end up having a large number > > > of small allocation areas free. The free_bytes sorting of chunks > > > leads to unnecessary checking of chunks that cannot satisfy the allocation. > > > Switch to contig_bits sorting to prevent scanning chunks that may > > > not be able to service the allocation request. > > > > > > Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx> > > > --- > > > mm/percpu.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/mm/percpu.c b/mm/percpu.c index > > > b40112b2fc59..c996bcffbb2a 100644 > > > --- a/mm/percpu.c > > > +++ b/mm/percpu.c > > > @@ -234,7 +234,7 @@ static int pcpu_chunk_slot(const struct > > > pcpu_chunk > > > *chunk) > > > if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || > chunk->contig_bits > > > == 0) > > > return 0; > > > > > > - return pcpu_size_to_slot(chunk->free_bytes); > > > + return pcpu_size_to_slot(chunk->contig_bits * > > > +PCPU_MIN_ALLOC_SIZE); > > > } > > > > > > /* set the pointer to a chunk in a page struct */ > > > > Reviewed-by: Peng Fan <peng.fan@xxxxxxx> > > > > Not relevant to this patch, another optimization to percpu might be > > good to use per chunk spin_lock, not gobal pcpu_lock. > > > > Percpu memory itself is expensive and for the most part shouldn't be part of > the critical path. Ideally, we don't have multiple chunks being allocated > simultaneously because once an allocation is given out, the chunk is pinned > until all allocations are freed. Thanks for clarification, since not critical patch, use global lock should be ok. Thanks, Peng. > > Thanks, > Dennis
