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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429952d5768sm27419982f8f.24.2025.10.29.07.45.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Oct 2025 07:45:15 -0700 (PDT) Message-ID: <85604399-40a8-4d13-809d-e5492e74a988@redhat.com> Date: Wed, 29 Oct 2025 15:45:14 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] ksm: perform a range-walk in break_ksm To: Pedro Demarchi Gomes , Andrew Morton Cc: Xu Xin , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251028131945.26445-1-pedrodemargomes@gmail.com> <20251028131945.26445-3-pedrodemargomes@gmail.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20251028131945.26445-3-pedrodemargomes@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28.10.25 14:19, Pedro Demarchi Gomes wrote: > Make break_ksm() receive an address range and change > break_ksm_pmd_entry() to perform a range-walk and return the address of > the first ksm page found. > > This change allows break_ksm() to skip unmapped regions instead of > iterating every page address. When unmerging large sparse VMAs, this > significantly reduces runtime, as confirmed by benchmark test (see > cover letter). Instead of referencing the cover letter, directly include the data here. > > Suggested-by: David Hildenbrand > Signed-off-by: Pedro Demarchi Gomes > --- > mm/ksm.c | 88 +++++++++++++++++++++++++++++++------------------------- > 1 file changed, 49 insertions(+), 39 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 2a9a7fd4c777..1d1ef0554c7c 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -607,34 +607,54 @@ static inline bool ksm_test_exit(struct mm_struct *mm) > return atomic_read(&mm->mm_users) == 0; > } > > -static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next, > +struct break_ksm_arg { > + unsigned long addr; > +}; You can avoid that by simply passing a pointer to addr. > + > +static int break_ksm_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned long end, > struct mm_walk *walk) > { > - struct page *page = NULL; > + struct page *page; > spinlock_t *ptl; > - pte_t *pte; > - pte_t ptent; > - int ret; > + pte_t *start_ptep = NULL, *ptep, pte; Is there a need to initialize start_ptep? > + int ret = 0; > + struct mm_struct *mm = walk->mm; > + struct break_ksm_arg *private = (struct break_ksm_arg *) walk->private; Prefer reverse xmas tree: struct break_ksm_arg *private = (struct break_ksm_arg *) walk->private; struct mm_struct *mm = walk->mm; ... With the break_ksm_arg simplification you'd had unsigned long *found_addr = (unsigned long *)walk->private; > > - pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); > - if (!pte) > + if (ksm_test_exit(walk->mm)) > return 0; > - ptent = ptep_get(pte); > - if (pte_present(ptent)) { > - page = vm_normal_page(walk->vma, addr, ptent); > - } else if (!pte_none(ptent)) { > - swp_entry_t entry = pte_to_swp_entry(ptent); > > - /* > - * As KSM pages remain KSM pages until freed, no need to wait > - * here for migration to end. > - */ > - if (is_migration_entry(entry)) > - page = pfn_swap_entry_to_page(entry); > + if (signal_pending(current)) > + return -ERESTARTSYS; I assume that's not a problem for the other callsites that wouldn't check this before. > + > + start_ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); > + if (!start_ptep) > + return 0; > + > + for (ptep = start_ptep; addr < end; ptep++, addr += PAGE_SIZE) { Best to declare pte and folio (see last mail) here in the loop: pte_t pte = ptep_get(ptep); struct folio *folio = NULL; > + pte = ptep_get(ptep); > + page = NULL; > + if (pte_present(pte)) { > + page = vm_normal_page(walk->vma, addr, pte); > + } else if (!pte_none(pte)) { > + swp_entry_t entry = pte_to_swp_entry(pte); > + > + /* > + * As KSM pages remain KSM pages until freed, no need to wait > + * here for migration to end. > + */ > + if (is_migration_entry(entry)) > + page = pfn_swap_entry_to_page(entry); > + } > + /* return 1 if the page is an normal ksm page or KSM-placed zero page */ > + ret = (page && folio_test_ksm(page_folio(page))) || is_ksm_zero_pte(pte); > + if (ret) { > + private->addr = addr; > + goto out_unlock; > + } I suggest you call "ret" "found" instead. > } > - /* return 1 if the page is an normal ksm page or KSM-placed zero page */ > - ret = (page && folio_test_ksm(page_folio(page))) || is_ksm_zero_pte(ptent); > - pte_unmap_unlock(pte, ptl); > +out_unlock: > + pte_unmap_unlock(ptep, ptl); > return ret; > } > > @@ -661,9 +681,11 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = { > * of the process that owns 'vma'. We also do not want to enforce > * protection keys here anyway. > */ > -static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma) > +static int break_ksm(struct vm_area_struct *vma, unsigned long addr, > + unsigned long end, bool lock_vma) > { > vm_fault_t ret = 0; > + struct break_ksm_arg break_ksm_arg; > const struct mm_walk_ops *ops = lock_vma ? > &break_ksm_lock_vma_ops : &break_ksm_ops; > > @@ -671,11 +693,10 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_v > int ksm_page; > > cond_resched(); > - ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL); > - if (WARN_ON_ONCE(ksm_page < 0)) > + ksm_page = walk_page_range_vma(vma, addr, end, ops, &break_ksm_arg); > + if (ksm_page <= 0) > return ksm_page; > - if (!ksm_page) > - return 0; > + addr = break_ksm_arg.addr; > ret = handle_mm_fault(vma, addr, > FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE, > NULL); > @@ -761,7 +782,7 @@ static void break_cow(struct ksm_rmap_item *rmap_item) > mmap_read_lock(mm); > vma = find_mergeable_vma(mm, addr); > if (vma) > - break_ksm(vma, addr, false); > + break_ksm(vma, addr, addr + 1, false); Better to use addr + PAGE_SIZE -- Cheers David / dhildenb