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Thu, 08 Dec 2022 10:08:01 -0800 (PST) MIME-Version: 1.0 References: <20221205175140.1543229-1-nphamcs@gmail.com> <20221205175140.1543229-3-nphamcs@gmail.com> In-Reply-To: From: Nhat Pham Date: Thu, 8 Dec 2022 10:07:49 -0800 Message-ID: Subject: Re: [PATCH v2 2/4] workingset: refactor LRU refault to expose refault recency check To: Yu Zhao Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bfoster@redhat.com, willy@infradead.org, kernel-team@meta.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 5, 2022 at 6:26 PM Yu Zhao wrote: > > On Mon, Dec 5, 2022 at 7:22 PM Nhat Pham wrote: > > > > On Mon, Dec 5, 2022 at 5:29 PM Yu Zhao wrote: > > > > > > On Mon, Dec 5, 2022 at 6:19 PM Nhat Pham wrote: > > > > > > > > On Mon, Dec 5, 2022 at 3:49 PM Yu Zhao wrote: > > > > > > > > > > On Mon, Dec 5, 2022 at 10:51 AM Nhat Pham wrote: > > > > > > > > > > > > In preparation for computing recently evicted pages in cachestat, > > > > > > refactor workingset_refault and lru_gen_refault to expose a helper > > > > > > function that would test if an evicted page is recently evicted. > > > > > > > > > > > > Signed-off-by: Nhat Pham > > > > > > --- > > > > > > include/linux/swap.h | 1 + > > > > > > mm/workingset.c | 143 +++++++++++++++++++++++++++++-------------- > > > > > > 2 files changed, 99 insertions(+), 45 deletions(-) > > > > > > > > > > > > diff --git a/include/linux/swap.h b/include/linux/swap.h > > > > > > index a18cf4b7c724..dae6f6f955eb 100644 > > > > > > --- a/include/linux/swap.h > > > > > > +++ b/include/linux/swap.h > > > > > > @@ -361,6 +361,7 @@ static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry) > > > > > > } > > > > > > > > > > > > /* linux/mm/workingset.c */ > > > > > > +bool workingset_test_recent(void *shadow, bool file, bool *workingset); > > > > > > void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages); > > > > > > void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg); > > > > > > void workingset_refault(struct folio *folio, void *shadow); > > > > > > diff --git a/mm/workingset.c b/mm/workingset.c > > > > > > index 79585d55c45d..44b331ce3040 100644 > > > > > > --- a/mm/workingset.c > > > > > > +++ 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. > > > > > > + */ > > > > > > +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))); > > > > > > +} > > > > > > > > > > Nit: not refactoring actually looks cleaner to me -- there are only a > > > > > few lines of duplicated code and you can get rid of 4 parameters > > > > > including the unused workingset in the next patch. > > > > > > > > (resending this because I forgot to forward to the rest of the > > > > group!) > > > > > > > > Thanks for the comment, Yu! > > > > > > > > Personally, I prefer refactoring this piece of logic - I do think that > > > > it is cleaner than copying the logic into the syscall implementation. > > > > > > Let me clarify. > > > > > > You can add > > > lru_gen_test_recent(void *shadow, bool file) > > > without refactoring the existing > > > lru_gen_refault(). > > > > > > Set the boilerplate aside, you only repeat one line of code, which is > > > the last line in the new function. > > > > > > (The boilerplate code is repeated in many places, and that's why it's > > > called boilerplate.) > > > > Oh maybe I've misunderstood your original comment. Your > > suggestion is to repeat the eviction recency check in workingset.c > > (i.e keep the *_gen_refault unchanged - just copy that logic to > > *_test_recent)? > > Correct. Thanks for the suggestion, Yu! I'll update if there are complications with this, but otherwise the change will be in v3 of this patch series.