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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Stat-Signature: d6q5iajtxncwzkpdw88sge6rn7onp13k X-Rspam-User: X-Rspamd-Queue-Id: 0A01DC000F X-HE-Tag: 1760433971-169917 X-HE-Meta: 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 OwwjDCuo 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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 14.10.25 07:58, Pedro Demarchi Gomes wrote: > Currently, scan_get_next_rmap_item() walks every page address in a VMA > to locate mergeable pages. This becomes highly inefficient when scanning > large virtual memory areas that contain mostly unmapped regions. > > This patch replaces the per-address lookup with a range walk using > walk_page_range(). The range walker allows KSM to skip over entire > unmapped holes in a VMA, avoiding unnecessary lookups. > > To evaluate this change, I created a test that maps a 1 TB virtual area > where only the first and last 10 MB are populated with identical data. > With this patch applied, KSM scanned and merged the region approximately > seven times faster. > > This problem was previously discussed in [1]. > > [1] https://lore.kernel.org/linux-mm/423de7a3-1c62-4e72-8e79-19a6413e420c@redhat.com/ > > Signed-off-by: Pedro Demarchi Gomes > --- > mm/ksm.c | 136 ++++++++++++++++++++++++++++++++----------------------- > 1 file changed, 79 insertions(+), 57 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 3aed0478fdce..584fd987e8ae 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -2455,15 +2455,80 @@ static bool should_skip_rmap_item(struct folio *folio, > return true; > } > > +struct ksm_walk_private { > + struct page *page; > + struct ksm_rmap_item *rmap_item; > + struct ksm_mm_slot *mm_slot; > +}; > + > +static int ksm_walk_test(unsigned long addr, unsigned long next, struct mm_walk *walk) > +{ > + struct vm_area_struct *vma = walk->vma; > + > + if (!vma || !(vma->vm_flags & VM_MERGEABLE)) The anon_vma check should go in here as well. How can we possibly get !vma? > + return 1; > + return 0; > +} > + > +static int ksm_pte_entry(pte_t *pte, unsigned long addr, > + unsigned long end, struct mm_walk *walk) > +{ > + struct mm_struct *mm = walk->mm; > + struct vm_area_struct *vma = walk->vma; > + struct ksm_walk_private *private = (struct ksm_walk_private *) walk->private; > + struct ksm_mm_slot *mm_slot = private->mm_slot; > + pte_t ptent = ptep_get(pte); > + struct page *page = pfn_to_online_page(pte_pfn(ptent)); Oh no. vm_normal_page() > + struct ksm_rmap_item *rmap_item; > + struct folio *folio; > + > + ksm_scan.address = addr; > + > + if (ksm_test_exit(mm)) > + return 1; > + > + if (!page) > + return 0; > + > + folio = page_folio(page); > + if (folio_is_zone_device(folio) || !folio_test_anon(folio)) > + return 0; > + > + folio_get(folio); > + > + flush_anon_page(vma, page, ksm_scan.address); > + flush_dcache_page(page); > + rmap_item = get_next_rmap_item(mm_slot, > + ksm_scan.rmap_list, ksm_scan.address); > + if (rmap_item) { > + ksm_scan.rmap_list = > + &rmap_item->rmap_list; > + > + if (should_skip_rmap_item(folio, rmap_item)) { > + folio_put(folio); > + return 0; > + } > + ksm_scan.address = end; > + private->page = page; > + } else > + folio_put(folio); > + You're under PTL, get_next_rmap_item() will perform an allocation, so that won't work. Observe how the original code worked around that by performing all magic outside of the PTL (folio_walk_end()). When you switch to .pmd_entry() (see below) you will be able to handle it. What you could also try doing is returing page+folio and letting the caller deal with everything starting at the flush_anon_page(). > + private->rmap_item = rmap_item; > + return 1; > +} > + > +struct mm_walk_ops walk_ops = { > + .pte_entry = ksm_pte_entry, > + .test_walk = ksm_walk_test, > + .walk_lock = PGWALK_RDLOCK, > +}; It's more complicated: you'd be remapping each PMD to be mapped by PTEs first, which is not what we want. You'll have to handle pmd_entry instead of pte_entry. > + > static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) > { > struct mm_struct *mm; > struct ksm_mm_slot *mm_slot; > struct mm_slot *slot; > - struct vm_area_struct *vma; > - struct ksm_rmap_item *rmap_item; > - struct vma_iterator vmi; > - int nid; > + int nid, ret; > > if (list_empty(&ksm_mm_head.slot.mm_node)) > return NULL; > @@ -2527,64 +2592,21 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) > > slot = &mm_slot->slot; > mm = slot->mm; > - vma_iter_init(&vmi, mm, ksm_scan.address); > > mmap_read_lock(mm); > if (ksm_test_exit(mm)) > goto no_vmas; > > - for_each_vma(vmi, vma) { > - if (!(vma->vm_flags & VM_MERGEABLE)) > - continue; > - if (ksm_scan.address < vma->vm_start) > - ksm_scan.address = vma->vm_start; > - if (!vma->anon_vma) > - ksm_scan.address = vma->vm_end; > - > - while (ksm_scan.address < vma->vm_end) { > - struct page *tmp_page = NULL; > - struct folio_walk fw; > - struct folio *folio; > - > - if (ksm_test_exit(mm)) > - break; > - > - folio = folio_walk_start(&fw, vma, ksm_scan.address, 0); > - if (folio) { > - if (!folio_is_zone_device(folio) && > - folio_test_anon(folio)) { > - folio_get(folio); > - tmp_page = fw.page; > - } > - folio_walk_end(&fw, vma); > - } > - > - if (tmp_page) { > - flush_anon_page(vma, tmp_page, ksm_scan.address); > - flush_dcache_page(tmp_page); > - rmap_item = get_next_rmap_item(mm_slot, > - ksm_scan.rmap_list, ksm_scan.address); > - if (rmap_item) { > - ksm_scan.rmap_list = > - &rmap_item->rmap_list; > - > - if (should_skip_rmap_item(folio, rmap_item)) { > - folio_put(folio); > - goto next_page; > - } > - > - ksm_scan.address += PAGE_SIZE; > - *page = tmp_page; > - } else { > - folio_put(folio); > - } > - mmap_read_unlock(mm); > - return rmap_item; > - } > -next_page: > - ksm_scan.address += PAGE_SIZE; > - cond_resched(); You're dropping all cond_resched(), which will be a problem. > - } > + struct ksm_walk_private walk_private = { > + .page = NULL, > + .rmap_item = NULL, > + .mm_slot = ksm_scan.mm_slot > + }; empty line missing > + ret = walk_page_range(mm, ksm_scan.address, -1, &walk_ops, (void *) &walk_private); > + *page = walk_private.page; > + if (ret) { > + mmap_read_unlock(mm); > + return walk_private.rmap_item; > } > > if (ksm_test_exit(mm)) { -- Cheers David / dhildenb