From: Nhat Pham <nphamcs@gmail.com>
To: Yu Zhao <yuzhao@google.com>
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
Subject: Re: [PATCH v2 2/4] workingset: refactor LRU refault to expose refault recency check
Date: Mon, 5 Dec 2022 18:22:11 -0800 [thread overview]
Message-ID: <CAKEwX=P=ypLfqmJYKP1BWYzjpMUMWGg4v=DfjnO5hR_qhQUmUQ@mail.gmail.com> (raw)
In-Reply-To: <CAOUHufZZX9TyTbZCbmOt9FeyNYxoDwVPOkM0=t3Nyz2ZtP-s7A@mail.gmail.com>
On Mon, Dec 5, 2022 at 5:29 PM Yu Zhao <yuzhao@google.com> wrote:
>
> On Mon, Dec 5, 2022 at 6:19 PM Nhat Pham <nphamcs@gmail.com> wrote:
> >
> > On Mon, Dec 5, 2022 at 3:49 PM Yu Zhao <yuzhao@google.com> wrote:
> > >
> > > On Mon, Dec 5, 2022 at 10:51 AM Nhat Pham <nphamcs@gmail.com> 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 <nphamcs@gmail.com>
> > > > ---
> > > > 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)?
next prev parent reply other threads:[~2022-12-06 2:22 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-05 17:51 [PATCH v2 0/4] cachestat: a new syscall for page cache state of files Nhat Pham
2022-12-05 17:51 ` [PATCH v2 1/4] workingset: fix confusion around eviction vs refault container Nhat Pham
2022-12-05 17:51 ` [PATCH v2 2/4] workingset: refactor LRU refault to expose refault recency check Nhat Pham
2022-12-05 23:49 ` Yu Zhao
2022-12-06 1:19 ` Nhat Pham
2022-12-06 1:28 ` Yu Zhao
2022-12-06 2:22 ` Nhat Pham [this message]
2022-12-06 2:25 ` Yu Zhao
2022-12-08 18:07 ` Nhat Pham
2022-12-06 15:22 ` Matthew Wilcox
2022-12-07 17:28 ` Nhat Pham
2022-12-05 17:51 ` [PATCH v2 3/4] cachestat: implement cachestat syscall Nhat Pham
2022-12-05 23:15 ` kernel test robot
2022-12-06 4:48 ` kernel test robot
2022-12-06 4:59 ` kernel test robot
2022-12-07 1:42 ` kernel test robot
2022-12-10 23:51 ` Al Viro
2022-12-12 13:22 ` Brian Foster
2022-12-12 16:50 ` Nhat Pham
2022-12-12 16:23 ` Nhat Pham
2022-12-12 16:24 ` Matthew Wilcox
2022-12-12 16:37 ` Nhat Pham
2022-12-05 17:51 ` [PATCH v2 4/4] selftests: Add selftests for cachestat Nhat Pham
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