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b=gkdoRuqf//KLfkKrg6Q0zNdKQozBKIooaO+H4LQ9d6+59qQL4vwYuvf8+K6Fj6ErM HCOGzhG5VuJih4z8gsTSol/cDmjTqpyYUeAa/0ejPT9qiZEj59HZboTs02C+MiTbhf 9ElVHrvr7AFdwHuu+WhDF2Aztq+L3iYuvo8l6dIQH2RB05V9CtJhj5MfVBkyz2em+V l2epQNCRK7Ogz/On6cC5mbCOskwglkDPHPsKWyfqkmY8WTlMJgS0SnEW3u/7pWyBT8 X8LgHADG6j+WwcL0F4xB2bjjHBTlwYGeVp6puD1s4QtvbVskK/GEzdhvxugb3JLddr IqK4srA+YpbYA== From: SeongJae Park To: Bijan Tabatabai Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, david@redhat.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, bijantabatab@micron.com, venkataravis@micron.com, emirakhur@micron.com, ajayjoshi@micron.com, vtavarespetr@micron.com Subject: Re: [RFC PATCH v2 2/2] mm/damon/paddr: Allow multiple migrate targets Date: Sat, 21 Jun 2025 11:02:15 -0700 Message-Id: <20250621180215.36243-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250620180458.5041-3-bijan311@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: fuj7t1omgs5mj4gg3n63fmydwr3uttez X-Rspamd-Queue-Id: 001CFA0005 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1750528938-583647 X-HE-Meta: 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 FGWOnYGp DhcWG1vkSeqnM47cYDwfF/BUB+rtQMxX4lvxMAmiD97Z/Ca00XuZ778EGMSY9xr79103g+USCP3p7E3OPLQVuavJIy6bdTtNkSTaXma86gE8J+1LLRZW3lNAsqD+uftsjZmVCPybB1sGtPiRUn5kodlKvrIapejlKBoTssgOwuUGBjWUFRS4vOP1dQHiGConk2GFAIRDNhN9RWYR9OSCeCVk9xnfo7eRRN6mp6kHanx3zIw175CJ22ANyxV0GvQx3HIHmZehNOXjjLg1yzi88U160AKKTnca0LO0VqL5vopYpKCY20y/uFJupHEH6gg1DfeRdWaIJKzW91BtMyY8RtYUqZ8gCV6DmaEd2EtwkO7Gt+oJkcY90VwDZx5KrnlGLlX2i X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Bijan, On Fri, 20 Jun 2025 13:04:58 -0500 Bijan Tabatabai wrote: > From: Bijan Tabatabai > > The migrate_{hot,cold} DAMONS actions take a parameter, target_nid, to > indicate what node the actions should migrate pages to. In this patch, > we allow passing in a list of migration targets into target_nid. When > this is done, the mirgate_{hot, cold} actions will migrate pages between > the specified nodes using the global interleave weights found at > /sys/kernel/mm/mempolicy/weighted_interleave/node. This functionality > can be used to dynamically adjust how pages are interleaved in response > to changes in bandwidth utilization to improve performance, as discussed > in [1]. When only a single migration target is passed to target_nid, the > migrate_{hot,cold} actions will act the same as before. [...] > include/linux/damon.h | 8 +-- > mm/damon/core.c | 9 ++-- > mm/damon/lru_sort.c | 2 +- > mm/damon/paddr.c | 108 +++++++++++++++++++++++++++++++++++++-- > mm/damon/reclaim.c | 2 +- > mm/damon/sysfs-schemes.c | 14 +++-- > samples/damon/mtier.c | 6 ++- > samples/damon/prcl.c | 2 +- > 8 files changed, 131 insertions(+), 20 deletions(-) If we keep pursuing making DAMON users be able to specify multiple migration destination nodes and their weights[1], I think we may need only paddr.c part change of this patch in the final version of this great work. [...] > static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s, > unsigned long *sz_filter_passed) > { > unsigned long addr, applied; > - LIST_HEAD(folio_list); > + struct rmap_walk_control rwc; [...] > > addr = r->ar.start; > while (addr < r->ar.end) { > @@ -522,15 +599,38 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s, > else > *sz_filter_passed += folio_size(folio); > > + /* > + * If there is only one target node, migrate there. Otherwise, > + * interleave across the nodes according to the global > + * interleave weights > + */ > + if (nr_nodes == 1) { > + target_nid = first_node(s->target_nids); > + } else { > + target_nid = NUMA_NO_NODE; > + /* Updates target_nid */ > + rmap_walk(folio, &rwc); > + } So we are doing rmap_walk(), which is known to be not very fast, for getting the target node id of this page, in a way very similar to that of weighted interleaving, right? I don't think we really need to behave that same to weighted interleaving with the cost. I'd hence suggest to implement and use a simple weights handling mechanism here. It could be roud-robin way, like weighted interleaving, or probabilistic way, using damon_rand(). The round-robin way may be simpler in my opinion. For example, unsigned int damos_pa_nid_to_migrate(struct damos_migrate_dest *dest) { static unsigned int nr_migrated = 0; unsigned int total_weight = 0; unsigned int weights_to_ignore; size_t i; for (i = 0; i < dest->nr_dests; i++) total_weight += dest->weight_arr[i]; weights_to_ignore = nr_migrate++ % total_weight; total_weight = 0; for (i = 0; i < dest->nr_dests; i++) { total_weight += dest->weight_arr[i]; if (total_weight >= weights_to_ignore) return dest->node_id_arr[i]; } WARN_ON_ONCE(1, "I don't know what I did wrong"); return 0; } Then, we could replace the above rmap_walk() call with this one. What do you think? Nothing stands out from other parts to me. I will do more thorough read on the next revision, though. [1] https://lore.kernel.org/20250621173639.35906-1-sj@kernel.org Thanks, SJ [...]