RE: [PATCH] blk-mq: remove the calling of local_memory_node()
From: Tianxianting <hidden>
Date: 2020-10-20 02:53:27
Also in:
lkml
Thanks Michal, Hi, raghavendra, Jens Could you help comment this issue? Thanks in advance. -----Original Message----- From: Michal Hocko [mailto:mhocko@suse.com] Sent: Monday, October 19, 2020 7:40 PM To: tianxianting (RD) <redacted> Cc: axboe@kernel.dk; raghavendra.kt@linux.vnet.ibm.com; linux-block@vger.kernel.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH] blk-mq: remove the calling of local_memory_node() On Mon 19-10-20 16:20:47, Xianting Tian wrote:
We don't need to check whether the node is memoryless numa node before calling allocator interface. SLUB(and SLAB,SLOB) relies on the page allocator to pick a node. Page allocator should deal with memoryless nodes just fine. It has zonelists constructed for each possible nodes. And it will automatically fall back into a node which is closest to the requested node. As long as __GFP_THISNODE is not enforced of course. The code comments of kmem_cache_alloc_node() of SLAB also showed this: * Fallback to other node is possible if __GFP_THISNODE is not set. blk-mq code doesn't set __GFP_THISNODE, so we can remove the calling of local_memory_node().
yes, this is indeed the case. I cannot really judge the blg-mq code but it seems to be unnecessary. Maybe there are some subtle details not explained by bffed457160ab though.
Fixes: bffed457160ab ("blk-mq: Avoid memoryless numa node encoded in
hctx numa_node")But the existing code is not broken. It just overdoes what needs to be done. So effectively bffed457160ab was not needed. I do not think that Fixes is really necessary.
quoted hunk ↗ jump to hunk
Signed-off-by: Xianting Tian <redacted> --- block/blk-mq-cpumap.c | 2 +- block/blk-mq.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c index0157f2b34..3db84d319 100644--- a/block/blk-mq-cpumap.c +++ b/block/blk-mq-cpumap.c@@ -89,7 +89,7 @@ int blk_mq_hw_queue_to_node(struct blk_mq_queue_map*qmap, unsigned int index) for_each_possible_cpu(i) { if (index == qmap->mq_map[i]) - return local_memory_node(cpu_to_node(i)); + return cpu_to_node(i); } return NUMA_NO_NODE;diff --git a/block/blk-mq.c b/block/blk-mq.c indexcdced4aca..48f8366b2 100644--- a/block/blk-mq.c +++ b/block/blk-mq.c@@ -2737,7 +2737,7 @@ static void blk_mq_init_cpu_queues(struct request_queue *q, for (j = 0; j < set->nr_maps; j++) { hctx = blk_mq_map_queue_type(q, j, i); if (nr_hw_queues > 1 && hctx->numa_node == NUMA_NO_NODE) - hctx->numa_node = local_memory_node(cpu_to_node(i)); + hctx->numa_node = cpu_to_node(i); } } } --2.17.1
-- Michal Hocko SUSE Labs