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From: Baoquan He To: Youngjun Park Cc: akpm@linux-foundation.org, chrisl@kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: Re: [PATCH v6 3/4] mm: memcontrol: add interfaces for swap tier selection Message-ID: References: <20260421055323.940344-1-youngjun.park@lge.com> <20260421055323.940344-4-youngjun.park@lge.com> Precedence: bulk X-Mailing-List: cgroups@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: <20260421055323.940344-4-youngjun.park@lge.com> X-Migadu-Flow: FLOW_OUT On 04/21/26 at 02:53pm, Youngjun Park wrote: ...snip... > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c3d98ab41f1f..0f67572e5e3e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -68,6 +68,7 @@ > #include > #include "slab.h" > #include "memcontrol-v1.h" > +#include "swap_tier.h" > > #include > > @@ -4130,6 +4131,8 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > refcount_set(&memcg->id.ref, 1); > css_get(css); > > + swap_tiers_memcg_inherit_mask(memcg); > + > /* > * Ensure mem_cgroup_from_private_id() works once we're fully online. > * > @@ -5667,6 +5670,88 @@ static int swap_events_show(struct seq_file *m, void *v) > return 0; > } > > +static int swap_tier_show(struct seq_file *m, void *v) > +{ > + struct mem_cgroup *memcg = mem_cgroup_from_seq(m); > + > + swap_tiers_mask_show(m, READ_ONCE(memcg->tier_mask)); > + return 0; > +} > + > +static ssize_t swap_tier_write(struct kernfs_open_file *of, > + char *buf, size_t nbytes, loff_t off) > +{ > + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); > + char *pos, *token; > + int ret = 0; > + int original_mask = 0; > + > + pos = strstrip(buf); > + > + spin_lock(&swap_tier_lock); > + if (!*pos) { > + WRITE_ONCE(memcg->tier_mask, TIER_ALL_MASK); > + goto sync; > + } > + > + original_mask = memcg->tier_mask; > + > + while ((token = strsep(&pos, " \t\n")) != NULL) { > + int mask; > + > + if (!*token) > + continue; > + > + if (token[0] != '-' && token[0] != '+') { > + ret = -EINVAL; > + goto err; > + } > + > + mask = swap_tiers_mask_lookup(token+1); > + if (!mask) { > + ret = -EINVAL; > + goto err; > + } > + > + /* > + * if child already set, cannot add that tiers for hierarch mismatching. > + * parent compatible, child must respect parent selected swap device. > + */ This paragraph of code comment sounds a little unnatural. We are writing it into memcg, the child memcg is handled in swap_tiers_memcg_sync_mask(), isn't it? I don't get the 2nd sentence. Could you help explain? > + switch (token[0]) { > + case '-': > + WRITE_ONCE(memcg->tier_mask, > + memcg->tier_mask & ~mask); > + break; > + case '+': > + WRITE_ONCE(memcg->tier_mask, > + memcg->tier_mask | mask); > + break; > + default: > + ret = -EINVAL; > + break; > + } > + > + if (ret) > + goto err; > + } > + > +sync: > + swap_tiers_memcg_sync_mask(memcg); > +err: > + if (ret) > + WRITE_ONCE(memcg->tier_mask, original_mask); > + spin_unlock(&swap_tier_lock); > + return ret ? ret : nbytes; > +} > + ...snip...