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Tue, 18 Feb 2025 14:25:15 -0800 (PST) X-Google-Smtp-Source: AGHT+IHbLdIDA7W8b7S7Vw5wFLoiCrmHVgVEE4AdNMwuOX5Ui1GwIyfL4fakzqmMyQ3bo2Fzq3h+smXl4DCCzGL6h+Q= X-Received: by 2002:a05:6902:a06:b0:e5d:cb35:59ad with SMTP id 3f1490d57ef6-e5e0a130d82mr1456780276.31.1739917515590; Tue, 18 Feb 2025 14:25:15 -0800 (PST) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250211003028.213461-1-npache@redhat.com> <20250211003028.213461-2-npache@redhat.com> <8d1fed22-5ba8-433b-9ef9-478b337b10d5@arm.com> In-Reply-To: <8d1fed22-5ba8-433b-9ef9-478b337b10d5@arm.com> From: Nico Pache Date: Tue, 18 Feb 2025 15:24:49 -0700 X-Gm-Features: AWEUYZncCSKg8r54HWOU0tx_q-3fZrZtewemdqSCm6AyoWEay7IYmb-RET1BGEU Message-ID: Subject: Re: [RFC v2 1/9] introduce khugepaged_collapse_single_pmd to unify khugepaged and madvise_collapse To: Ryan Roberts Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, dev.jain@arm.com, sunnanyong@huawei.com, usamaarif642@gmail.com, audra@redhat.com, akpm@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, tiwai@suse.de X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: XfrGscfpAwUE1ZCTj6sMxaNbe9CNbMPkJLrHdXXC4dI_1739917516 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Feb 18, 2025 at 9:26=E2=80=AFAM Ryan Roberts = wrote: > > On 11/02/2025 00:30, Nico Pache wrote: > > The khugepaged daemon and madvise_collapse have two different > > implementations that do almost the same thing. > > > > Create khugepaged_collapse_single_pmd to increase code > > reuse and create an entry point for future khugepaged changes. > > > > Refactor madvise_collapse and khugepaged_scan_mm_slot to use > > the new khugepaged_collapse_single_pmd function. > > > > Signed-off-by: Nico Pache > > --- > > mm/khugepaged.c | 96 +++++++++++++++++++++++++------------------------ > > 1 file changed, 50 insertions(+), 46 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 5f0be134141e..46faee67378b 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -2365,6 +2365,52 @@ static int hpage_collapse_scan_file(struct mm_st= ruct *mm, unsigned long addr, > > } > > #endif > > > > +/* > > + * Try to collapse a single PMD starting at a PMD aligned addr, and re= turn > > + * the results. > > + */ > > +static int khugepaged_collapse_single_pmd(unsigned long addr, struct m= m_struct *mm, > > + struct vm_area_struct *vma, bool *mmap= _locked, > > + struct collapse_control *cc) > > nit: given the vma links to the mm is it really neccessary to pass both? = Why not > just pass vma? Ah good point! > > > +{ > > + int result =3D SCAN_FAIL; > > + unsigned long tva_flags =3D cc->is_khugepaged ? TVA_ENFORCE_SYSFS= : 0; > > + > > + if (!*mmap_locked) { > > + mmap_read_lock(mm); > > + *mmap_locked =3D true; > > + } > > AFAICT, the read lock is always held when khugepaged_collapse_single_pmd(= ) is > called. Perhaps VM_WARN_ON(!*mmap_locked) would be more appropriate? Hmm, I'm actually not sure why that's there. Its probably left over from a previous change I was trying a while back. > > > + > > + if (thp_vma_allowable_order(vma, vma->vm_flags, > > + tva_flags, PMD_ORDER)) { > > + if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) { > > I guess it was like this before, but what's the relevance of CONFIG_SHMEM= ? > Surely this should work for any file if CONFIG_READ_ONLY_THP_FOR_FS is en= abled? Yeah I think David brought up a similar point during one of our meetings. I'm just combining the collapse users, so I'll leave it for now. > > > + 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; > > + result =3D hpage_collapse_scan_file(mm, addr, fil= e, pgoff, > > + cc); > > + fput(file); > > + if (result =3D=3D SCAN_PTE_MAPPED_HUGEPAGE) { > > + mmap_read_lock(mm); > > + if (hpage_collapse_test_exit_or_disable(m= m)) > > + goto end; > > + result =3D collapse_pte_mapped_thp(mm, ad= dr, > > + !cc->is_= khugepaged); > > + mmap_read_unlock(mm); > > + } > > + } else { > > + result =3D hpage_collapse_scan_pmd(mm, vma, addr, > > + mmap_locked, cc)= ; > > + } > > + if (result =3D=3D SCAN_SUCCEED || result =3D=3D SCAN_PMD_= MAPPED) > > + ++khugepaged_pages_collapsed; > > Looks like this counter was previously only incremented for the scan path= , not > for the madvise_collapse path. Not sure if that's a problem? Yep! Usama noted that too, already fixed in the next version :) Thanks! -- Nico > > Thanks, > Ryan > > > + } > > +end: > > + return result; > > +} > > + > > static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *r= esult, > > struct collapse_control *cc) > > __releases(&khugepaged_mm_lock) > > @@ -2439,33 +2485,9 @@ static unsigned int khugepaged_scan_mm_slot(unsi= gned int pages, int *result, > > VM_BUG_ON(khugepaged_scan.address < hstart || > > khugepaged_scan.address + HPAGE_PMD_SIZ= E > > > hend); > > - if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous= (vma)) { > > - struct file *file =3D get_file(vma->vm_fi= le); > > - pgoff_t pgoff =3D linear_page_index(vma, > > - khugepaged_scan.address); > > > > - mmap_read_unlock(mm); > > - mmap_locked =3D false; > > - *result =3D hpage_collapse_scan_file(mm, > > - khugepaged_scan.address, file, pg= off, cc); > > - fput(file); > > - if (*result =3D=3D SCAN_PTE_MAPPED_HUGEPA= GE) { > > - mmap_read_lock(mm); > > - if (hpage_collapse_test_exit_or_d= isable(mm)) > > - goto breakouterloop; > > - *result =3D collapse_pte_mapped_t= hp(mm, > > - khugepaged_scan.address, = false); > > - if (*result =3D=3D SCAN_PMD_MAPPE= D) > > - *result =3D SCAN_SUCCEED; > > - mmap_read_unlock(mm); > > - } > > - } else { > > - *result =3D hpage_collapse_scan_pmd(mm, v= ma, > > - khugepaged_scan.address, &mmap_lo= cked, cc); > > - } > > - > > - if (*result =3D=3D SCAN_SUCCEED) > > - ++khugepaged_pages_collapsed; > > + *result =3D khugepaged_collapse_single_pmd(khugep= aged_scan.address, > > + mm, vma, &mmap_locked, cc= ); > > > > /* move to next address */ > > khugepaged_scan.address +=3D HPAGE_PMD_SIZE; > > @@ -2785,36 +2807,18 @@ int madvise_collapse(struct vm_area_struct *vma= , struct vm_area_struct **prev, > > mmap_assert_locked(mm); > > memset(cc->node_load, 0, sizeof(cc->node_load)); > > nodes_clear(cc->alloc_nmask); > > - if (IS_ENABLED(CONFIG_SHMEM) && !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; > > - result =3D hpage_collapse_scan_file(mm, addr, fil= e, pgoff, > > - cc); > > - fput(file); > > - } else { > > - result =3D hpage_collapse_scan_pmd(mm, vma, addr, > > - &mmap_locked, cc= ); > > - } > > + result =3D khugepaged_collapse_single_pmd(addr, mm, vma, = &mmap_locked, cc); > > + > > if (!mmap_locked) > > *prev =3D NULL; /* Tell caller we dropped mmap_l= ock */ > > > > -handle_result: > > switch (result) { > > case SCAN_SUCCEED: > > case SCAN_PMD_MAPPED: > > ++thps; > > break; > > case SCAN_PTE_MAPPED_HUGEPAGE: > > - BUG_ON(mmap_locked); > > - BUG_ON(*prev); > > - mmap_read_lock(mm); > > - result =3D collapse_pte_mapped_thp(mm, addr, true= ); > > - mmap_read_unlock(mm); > > - goto handle_result; > > - /* Whitelisted set of results where continuing OK */ > > case SCAN_PMD_NULL: > > case SCAN_PTE_NON_PRESENT: > > case SCAN_PTE_UFFD_WP: >