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Fri, 26 Jul 2024 03:04:54 -0700 (PDT) MIME-Version: 1.0 References: <20240726082818.260008-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Fri, 26 Jul 2024 22:04:42 +1200 Message-ID: Subject: Re: [PATCH] mm: huge_memory: don't start_stop_khugepaged for non-PMD THP To: David Hildenbrand Cc: Ryan Roberts , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Lance Yang , Baolin Wang , Yang Shi , Zi Yan Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4EDC31C0028 X-Stat-Signature: raqxcissae6jnq3rbt5gje6y8keqdzyq X-Rspam-User: X-HE-Tag: 1721988295-546770 X-HE-Meta: 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 Kq1b6Qa/ 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 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: On Fri, Jul 26, 2024 at 9:48=E2=80=AFPM David Hildenbrand wrote: > > On 26.07.24 11:43, Ryan Roberts wrote: > > On 26/07/2024 09:28, Barry Song wrote: > >> From: Barry Song > >> > >> khugepaged will be automatically started when PMD-sized THP is enabled > >> (either of the per-size anon control or the top-level control are set > >> to "always" or "madvise"), and it'll be automatically shutdown when > >> PMD-sized THP is disabled (when both the per-size anon control and the > >> top-level control are "never"). > >> > >> It seems unnecessary to call start_stop_khugepaged() for non-PMD THP, > >> as it would only waste CPU time. > >> > >> Cc: Lance Yang > >> Cc: Ryan Roberts > >> Cc: Baolin Wang > >> Cc: David Hildenbrand > >> Cc: Yang Shi > >> Cc: Zi Yan > >> Signed-off-by: Barry Song > >> --- > >> mm/huge_memory.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c > >> index 41460847988c..bd365e35acf7 100644 > >> --- a/mm/huge_memory.c > >> +++ b/mm/huge_memory.c > >> @@ -514,7 +514,7 @@ static ssize_t thpsize_enabled_store(struct kobjec= t *kobj, > >> } else > >> ret =3D -EINVAL; > >> > >> - if (ret > 0) { > >> + if (ret > 0 && order =3D=3D HPAGE_PMD_ORDER) { > >> int err; > >> > >> err =3D start_stop_khugepaged(); > > > > Personally I see this as a bit of a layering violation; its > > start_stop_khugepaged() that should decide the policy for when to start= and stop > > the daemon. thpsize_enabled_store() should just be calling > > start_stop_khugepaged() to notify that something potentially pertinent = to the a > > policy decision has changed. > My impression is that it slightly deviates from the huge page documentation= in Documentation/admin-guide/mm/transhuge.rst. khugepaged will be automatically started when PMD-sized THP is enabled (either of the per-size anon control or the top-level control are set to "always" or "madvise"), and it'll be automatically shutdown when PMD-sized THP is disabled (when both the per-size anon control and the top-level control are "never"). non-PMD size is not involved in khugepaged, but I agree the policy might ch= ange in the future. > Agreed, skimming the subject I was under the impression that we would be > fixing something here. working on another swapin_enabled and reviewing the enabled source code. I don't need this startstop for all sizes in that case, so I made a quick adjustment to this part as well. If neither of you likes it, that's fine with me :-) > > -- > Cheers, > > David / dhildenb > Thanks Barry