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From: Hao Li To: Harry Yoo Cc: "Vlastimil Babka (SUSE)" , akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/slub: allocate sheaves on local memory nodes Message-ID: References: <20260601095706.106551-1-hao.li@linux.dev> <33506b25-ab2f-4f31-a380-7c0fe65567a3@kernel.org> <5d8abe93-edd1-4b18-9ea4-7731dc831223@kernel.org> <380dc696-7184-4ce8-8650-e5f49127390c@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <380dc696-7184-4ce8-8650-e5f49127390c@kernel.org> X-Migadu-Flow: FLOW_OUT On Wed, Jun 10, 2026 at 10:49:26AM +0900, Harry Yoo wrote: > > > On 6/9/26 7:14 PM, Vlastimil Babka (SUSE) wrote: > > On 6/9/26 05:41, Harry Yoo wrote: > >> On 6/3/26 1:26 PM, Hao Li wrote: > >>> On Mon, Jun 01, 2026 at 08:28:16PM +0900, Harry Yoo wrote: > >>>> On 6/1/26 6:56 PM, Hao Li wrote: > >>>>> Sheaf structs are exchanged through node-local barns. Since barn structs > >>>>> are already allocated from their local NUMA node, this patch aims to > >>>>> allocate sheaf structs from their local memory nodes as well. > >>>>> > >>>>> To achieve this, the obvious choice would be using cpu_to_mem(). > >>>>> However, init_percpu_sheaves() and bootstrap_cache_sheaves() iterate > >>>>> through possible CPUs, whereas cpu_to_mem() is only initialized for > >>>>> online CPUs. Therefore, we cannot use cpu_to_mem() and instead need to > >>>>> use local_memory_node(cpu_to_node(cpu)), similar to what > >>>>> __build_all_zonelists() does. > >>>>> > >>>>> The primary goal of this patch is to improve NUMA node locality. > >>>>> Although the actual performance impact is minor, it still yields a ~1% > >>>>> improvement on a 192-core, 8-NUMA-node system when testing with the > >>>>> will-it-scale mmap test case. > >>>> > >>>> Oh, nice :) > >>>> > >>>> I have a question though... > >>>> > >>>> I wonder if would be better to handle this by e.g.) not returning empty > >>>> sheaves back to barn and freeing them if the node id doesn't match and > >>>> it's not a memoryless node. > >>>> > >>>> init_percpu_sheaves() and bootstrap_cache_sheaves() are not the only > >>>> places that can allocate sheaves from remote nodes; sheaves allocation > >>>> could fall back to other nodes and then SLUB could keep reusing those > >>>> sheaves from remote nodes even after memory is reclaimed. > >>> > >>> This is a good catch. In addition to the fallback mechanism, task migration > >>> between CPUs in __pcs_replace_empty_main() and __pcs_replace_full_main() can > >>> also mix up sheaf structs across different barns. So yeah, changing allocation > >>> locality is not a silver bullet. > >>> > >>>> If this works well, we probably don't need to handle it in > >>>> init_percpu_sheaves() and bootstrap_cache_sheaves() at all as they will > >>>> eventually be freed, while covering the other case too? > >>> > >>> freeing the empty sheaf if the NUMA node mismatches instead of putting it back > >>> into the barn is indeed a good idea. I like it. But unfortunately, my testing > >>> didn't show a clear performance improvement, though there was no noticeable > >>> degradation either. :-( > >> > >> Hmm... the idea still makes sense to me, but yeah, it's not late to fix > >> it when we have data to back up. > > > > I think if that approach doesn't complicate things unreasonably, it makes > > sense to do it even if there are no clear wins (as long as there are no > > regressions). > > I'm fine with that unless it introduces regressions or the > implementation complicates things too much :) > > What do you say, Hao? > Sure thing, let me test it thoroughly! -- Thanks, Hao