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Mon, 05 Apr 2021 11:20:59 -0700 (PDT) MIME-Version: 1.0 References: <20210404153311.1460106-1-yanfei.xu@windriver.com> <20210404153311.1460106-3-yanfei.xu@windriver.com> In-Reply-To: <20210404153311.1460106-3-yanfei.xu@windriver.com> From: Yang Shi Date: Mon, 5 Apr 2021 11:20:47 -0700 Message-ID: Subject: Re: [PATCH 2/2] mm: khugepaged: check MMF_DISABLE_THP ahead of iterating over vmas To: yanfei.xu@windriver.com Cc: Linux MM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: CE3CBE0001B4 X-Stat-Signature: bwqc1p75tzppsuhe8531hcouti43981c X-Rspamd-Server: rspam02 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=mail-ed1-f42.google.com; client-ip=209.85.208.42 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617646858-552709 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: On Sun, Apr 4, 2021 at 8:33 AM wrote: > > From: Yanfei Xu > > We could check MMF_DISABLE_THP ahead of iterating over all of vma. > Otherwise if some mm_struct contain a large number of vma, there will > be amounts meaningless cpu cycles cost. > > BTW, drop an unnecessary cond_resched(), because there is a another > cond_resched() followed it and no consumed invocation between them. > > Signed-off-by: Yanfei Xu > --- > mm/khugepaged.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 2efe1d0c92ed..c293ec4a94ea 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2094,6 +2094,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > */ > if (unlikely(!mmap_read_trylock(mm))) > goto breakouterloop_mmap_lock; > + if (test_bit(MMF_DISABLE_THP, &mm->flags)) > + goto breakouterloop_mmap_lock; It is fine to check this flag. But mmap_lock has been acquired so you should jump to breakouterloop. > if (likely(!khugepaged_test_exit(mm))) > vma = find_vma(mm, khugepaged_scan.address); > > @@ -2101,7 +2103,6 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > for (; vma; vma = vma->vm_next) { > unsigned long hstart, hend; > > - cond_resched(); I don't have a strong opinion for removing this cond_resched(). But IIUC khugepaged is a best effort job there is no harm to keep it IMHO. > if (unlikely(khugepaged_test_exit(mm))) { > progress++; > break; > -- > 2.27.0 > >