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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pTiRp-00AuBi-65; Sun, 19 Feb 2023 12:05:41 +0000 Date: Sun, 19 Feb 2023 12:05:41 +0000 From: Matthew Wilcox To: Nhat Pham Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bfoster@redhat.com, arnd@arndb.de, linux-api@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v10 1/3] workingset: refactor LRU refault to expose refault recency check Message-ID: References: <20230219073318.366189-1-nphamcs@gmail.com> <20230219073318.366189-2-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230219073318.366189-2-nphamcs@gmail.com> X-Rspam-User: X-Rspamd-Queue-Id: A0D5716000C X-Rspamd-Server: rspam01 X-Stat-Signature: n7gkuc741fcr4t5o6tq6ahkf6h9xx53n X-HE-Tag: 1676808349-909261 X-HE-Meta: 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 93/lIhxu 2Ft7iGNj/8bnu4f7GYx0GQoHCsZTuzEK6FfZbzuHFs3WwqA5FRhlu3fexou+fQZtvyWTEWSWcNZ4iTfGJhNYaMF8956kEwLvSq5s7FsU32lp/t0+iOredGc0BgOKl1AsiaoJAe2aghD8tjbC5OH7cjz872w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Feb 18, 2023 at 11:33:16PM -0800, Nhat Pham wrote: > +++ b/mm/workingset.c > @@ -244,6 +244,30 @@ static void *lru_gen_eviction(struct folio *folio) > return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs); > } > > +/* > + * Test if the folio is recently evicted. > + * > + * As a side effect, also populates the references with > + * values unpacked from the shadow of the evicted folio. > + */ I find this comment hard to understand. First it talks about "the folio", but it doesn't pass a folio. Then it talks about "the references", but I don't have any idea what those are either. I think what you mean is, * Test if the shadow entry is for a folio which was recently evicted. * Fills in @memcgid, @pgdat, @token and @workingset with values * extracted from the shadow entry. > +static bool lru_gen_test_recent(void *shadow, bool file, int *memcgid, > + struct pglist_data **pgdat, unsigned long *token, bool *workingset) > +{ > + struct mem_cgroup *eviction_memcg; > + struct lruvec *lruvec; > + struct lru_gen_struct *lrugen; > + unsigned long min_seq; > + > + unpack_shadow(shadow, memcgid, pgdat, token, workingset); > + eviction_memcg = mem_cgroup_from_id(*memcgid); > + > + lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat); > + lrugen = &lruvec->lrugen; > + > + min_seq = READ_ONCE(lrugen->min_seq[file]); > + return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)); > +} [...] > +/* > + * Test if the folio is recently evicted by checking if > + * refault distance of shadow exceeds workingset size. > * > - * Calculates and evaluates the refault distance of the previously > - * evicted folio in the context of the node and the memcg whose memory > - * pressure caused the eviction. > + * As a side effect, populate workingset with the value > + * unpacked from shadow. > */ 1. Shouldn't this be kernel-doc? 2. Again, don't use the term "side effect" here. It's just one of the things that the function _does_.