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Thu, 26 Feb 2026 12:21:24 -0800 (PST) X-Received: by 2002:a05:690e:1a85:b0:64a:cee0:fa8 with SMTP id 956f58d0204a3-64cc23434b1mr419253d50.88.1772137283976; Thu, 26 Feb 2026 12:21:23 -0800 (PST) MIME-Version: 1.0 References: <20260226012929.169479-1-npache@redhat.com> <20260226012929.169479-6-npache@redhat.com> <60e44957-b816-4f7e-b004-4e957a67fe12@linux.alibaba.com> In-Reply-To: <60e44957-b816-4f7e-b004-4e957a67fe12@linux.alibaba.com> From: Nico Pache Date: Thu, 26 Feb 2026 13:20:57 -0700 X-Gm-Features: AaiRm53Me-8fM5QXkOAdd9G9REAo0qDWjRpQ1RLCmd1oOD2Zvo593rtgeJ1DgoI Message-ID: Subject: Re: [PATCH mm-unstable v2 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() To: Baolin Wang Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 6umhsh9rhnfXWDB0h69KXlrYZxArF5gyUZPY9m_R7eY_1772137284 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: E1C0E40013 X-Stat-Signature: igm5hbphiyfgp113ydi7eehjcz3knjqe X-Rspam-User: X-HE-Tag: 1772137287-903050 X-HE-Meta: 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 sDFsNjoU IwCTnSSIXddKMm9dyUZ8ljqN43/jpX/xUtqRtfkNhontVMpeM21ie+gtJIK1UKdOuWDEnAf8uodDA6HJe500mecNkeZl1rXkD22o9kizWhvlIsK4BA/CmyTGNyJwkZUwtj88pLZ3qGCjIxoXCeb/rL1Rdwen3Z64V/4ind3JjQxzpBX4Pgwg2aT7vKU7/mhxquxRXkAvHtqy0FT3/2AwNQm/kDhvG3kOVpZut2202ctZ3qS6Lf2yQFYaLXYKKvftNQE9Jo9UNMiztp9KiRzkUR/4KxyoVH7hCOjF9Y7UW9wFVTgzJvWsq+Rfinop7sw5pdwgRppFO/KCFpWp72etQiMiLU7bU+dapAWpssDtqNzOfgXoNuCJn3qAP9SQvqaxYHGMyvMngvp7hPC9MmA3HDqJyhbsOHCUAgf1P+3WwyvPMUh/jozhLw+6l7lJaI/Qm4GT49NFLR2gclvTPk6qQh+/DletnHWr+EhSANxQ+uc1EEyE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Feb 26, 2026 at 2:24=E2=80=AFAM Baolin Wang wrote: > > > > On 2/26/26 9:29 AM, Nico Pache wrote: > > The khugepaged daemon and madvise_collapse have two different > > implementations that do almost the same thing. > > > > Create collapse_single_pmd to increase code reuse and create an entry > > point to these two users. > > > > Refactor madvise_collapse and collapse_scan_mm_slot to use the new > > collapse_single_pmd function. This introduces a minor behavioral change > > that is most likely an undiscovered bug. The current implementation of > > khugepaged tests collapse_test_exit_or_disable before calling > > collapse_pte_mapped_thp, but we weren't doing it in the madvise_collaps= e > > case. By unifying these two callers madvise_collapse now also performs > > this check. We also modify the return value to be SCAN_ANY_PROCESS whic= h > > properly indicates that this process is no longer valid to operate on. > > > > We also guard the khugepaged_pages_collapsed variable to ensure its onl= y > > incremented for khugepaged. > > > > Reviewed-by: Lorenzo Stoakes > > Signed-off-by: Nico Pache > > --- > > [snip] > > > for (addr =3D hstart; addr < hend; addr +=3D HPAGE_PMD_SIZE) { > > enum scan_result result =3D SCAN_FAIL; > > - bool triggered_wb =3D false; > > > > -retry: > > if (!mmap_locked) { > > cond_resched(); > > mmap_read_lock(mm); > > mmap_locked =3D true; > > + *lock_dropped =3D true; > IIUC, this should be '*lock_dropped =3D false', right? Yes! Thanks for catching that :) As David and others have pointed out, this lock handling here might be unnecessary and better placed in collapse_single_pmd(). I meant to look into that before posting this but it slipped my mind. > > > result =3D hugepage_vma_revalidate(mm, addr, fals= e, &vma, > > cc); > > if (result !=3D SCAN_SUCCEED) { > > @@ -2836,46 +2872,20 @@ int madvise_collapse(struct vm_area_struct *vma= , unsigned long start, > > hend =3D min(hend, vma->vm_end & HPAGE_PMD_MASK); > > } > > mmap_assert_locked(mm); > > - if (!vma_is_anonymous(vma)) { > > - struct file *file =3D get_file(vma->vm_file); > > - pgoff_t pgoff =3D linear_page_index(vma, addr); > > - > > - mmap_read_unlock(mm); > > - mmap_locked =3D false; > > - *lock_dropped =3D true; > > - result =3D collapse_scan_file(mm, addr, file, pgo= ff, NULL, cc); > > > > - if (result =3D=3D SCAN_PAGE_DIRTY_OR_WRITEBACK &&= !triggered_wb && > > - mapping_can_writeback(file->f_mapping)) { > > - loff_t lstart =3D (loff_t)pgoff << PAGE_S= HIFT; > > - loff_t lend =3D lstart + HPAGE_PMD_SIZE -= 1; > > + result =3D collapse_single_pmd(addr, vma, &mmap_locked, N= ULL, cc); > > > > - filemap_write_and_wait_range(file->f_mapp= ing, lstart, lend); > > - triggered_wb =3D true; > > - fput(file); > > - goto retry; > > - } > > - fput(file); > > - } else { > > - result =3D collapse_scan_pmd(mm, vma, addr, &mmap= _locked, NULL, cc); > > - } > > if (!mmap_locked) > > *lock_dropped =3D true; > > > > -handle_result: > > switch (result) { > > case SCAN_SUCCEED: > > case SCAN_PMD_MAPPED: > > ++thps; > > break; > > - case SCAN_PTE_MAPPED_HUGEPAGE: > > - BUG_ON(mmap_locked); > > - mmap_read_lock(mm); > > - result =3D try_collapse_pte_mapped_thp(mm, addr, = true); > > - mmap_read_unlock(mm); > > - goto handle_result; > > /* Whitelisted set of results where continuing OK */ > > case SCAN_NO_PTE_TABLE: > > + case SCAN_PTE_MAPPED_HUGEPAGE: > > case SCAN_PTE_NON_PRESENT: > > case SCAN_PTE_UFFD_WP: > > case SCAN_LACK_REFERENCED_PAGE: >