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AJvYcCU4s1hNsKMbT3bIQ6AXHf+Wsk+6Q7v36hqjyQmds4Sv/3cS0uz44MGuXUnaHRqodU5RO9obT1gzvQcthMk66ekfn5U= X-Gm-Message-State: AOJu0Yx3DzVdTxWODtiF/tsb23MZ/l2AOk4K9aYdOZCJST6Quq3Dw1fm Xr9htN6eT59JN2KL3UjweP2mPoptWbMSbuqxvoIRykVuJDGrzHLZpPgR4sedbQ+WsjLkMnOgsCu 2QMcREVLWKBtuZsIeICsGYKAq+UI= X-Google-Smtp-Source: AGHT+IECl7hOsYW40Y45gV1sm9Ytj58js8VudwCqI2NFWpL1iSFcuXN1PTrg/XYWifynnUbTGy+eShGLDdOhm9ZDNi4= X-Received: by 2002:a17:90a:e550:b0:29a:7fde:7087 with SMTP id ei16-20020a17090ae55000b0029a7fde7087mr1573643pjb.8.1708739210543; Fri, 23 Feb 2024 17:46:50 -0800 (PST) MIME-Version: 1.0 References: <20240129054551.57728-1-ioworker0@gmail.com> In-Reply-To: <20240129054551.57728-1-ioworker0@gmail.com> From: Yang Shi Date: Fri, 23 Feb 2024 17:46:38 -0800 Message-ID: Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE_THP check To: Lance Yang Cc: akpm@linux-foundation.org, mhocko@suse.com, zokeefe@google.com, david@redhat.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: g84trry7f5qan8wx8gmei46c3fhbqpet X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CAAB81C0004 X-Rspam-User: X-HE-Tag: 1708739211-706672 X-HE-Meta: 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 Zd1R67su 3Ns7hQwgKIbNVQJmSd3xwMWOfgYNl2/52jqW7Q6AcbN6+CPQA3RBXRnwT+y+S/S353bzQk5f21yVT+rfcxVA4OQT1mQ== 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 Sun, Jan 28, 2024 at 9:46=E2=80=AFPM Lance Yang wr= ote: > > khugepaged scans the entire address space in the > background for each given mm, looking for > opportunities to merge sequences of basic pages > into huge pages. However, when an mm is inserted > to the mm_slots list, and the MMF_DISABLE_THP flag > is set later, this scanning process becomes > unnecessary for that mm and can be skipped to avoid > redundant operations, especially in scenarios with > a large address space. > > This commit introduces a check before each scanning > process to test the MMF_DISABLE_THP flag for the > given mm; if the flag is set, the scanning process > is bypassed, thereby improving the efficiency of > khugepaged. > > Signed-off-by: Lance Yang > --- > mm/khugepaged.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 2b219acb528e..d6a700834edc 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -410,6 +410,12 @@ static inline int hpage_collapse_test_exit(struct mm= _struct *mm) > return atomic_read(&mm->mm_users) =3D=3D 0; > } > > +static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *= mm) > +{ > + return hpage_collapse_test_exit(mm) || > + test_bit(MMF_DISABLE_THP, &mm->flags); > +} > + > void __khugepaged_enter(struct mm_struct *mm) > { > struct khugepaged_mm_slot *mm_slot; > @@ -1422,7 +1428,7 @@ static void collect_mm_slot(struct khugepaged_mm_sl= ot *mm_slot) > > lockdep_assert_held(&khugepaged_mm_lock); > > - if (hpage_collapse_test_exit(mm)) { > + if (hpage_collapse_test_exit_or_disable(mm)) { I'm not quite sure whether we should remove the mm from mm_slot and drop mm_count or not since clearing MMF_THP_DISABLE flag doesn't add the mm back. Creating new vma may add the mm back, but I don't think the behavior should depend on this. > /* free mm_slot */ > hash_del(&slot->hash); > list_del(&slot->mm_node); > @@ -2360,7 +2366,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > goto breakouterloop_mmap_lock; > > progress++; > - if (unlikely(hpage_collapse_test_exit(mm))) > + if (unlikely(hpage_collapse_test_exit_or_disable(mm))) > goto breakouterloop; > > vma_iter_init(&vmi, mm, khugepaged_scan.address); > @@ -2368,7 +2374,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > unsigned long hstart, hend; > > cond_resched(); > - if (unlikely(hpage_collapse_test_exit(mm))) { > + if (unlikely(hpage_collapse_test_exit_or_disable(mm))) { > progress++; > break; > } > @@ -2390,7 +2396,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > bool mmap_locked =3D true; > > cond_resched(); > - if (unlikely(hpage_collapse_test_exit(mm))) > + if (unlikely(hpage_collapse_test_exit_or_disable(= mm))) > goto breakouterloop; > > VM_BUG_ON(khugepaged_scan.address < hstart || > @@ -2408,7 +2414,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > fput(file); > if (*result =3D=3D SCAN_PTE_MAPPED_HUGEPA= GE) { > mmap_read_lock(mm); > - if (hpage_collapse_test_exit(mm)) > + if (hpage_collapse_test_exit_or_d= isable(mm)) > goto breakouterloop; > *result =3D collapse_pte_mapped_t= hp(mm, > khugepaged_scan.address, = false); > @@ -2450,7 +2456,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > * Release the current mm_slot if this mm is about to die, or > * if we scanned all vmas of this mm. > */ > - if (hpage_collapse_test_exit(mm) || !vma) { > + if (hpage_collapse_test_exit_or_disable(mm) || !vma) { Same like the above comment. In addition, didn't you need to change hpage_collapse_test_exit() to hpage_collapse_test_exit_or_disable() in hugepage_vma_revalidate()? > /* > * Make sure that if mm_users is reaching zero while > * khugepaged runs here, khugepaged_exit will find > -- > 2.33.1 >