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[2003:d8:2f0c:c200:fa4a:c4ff:1b32:21ce]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-427f009a9a9sm14833265f8f.29.2025.10.20.02.38.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Oct 2025 02:38:50 -0700 (PDT) Message-ID: <21e3ae2b-c441-4403-aac7-d9b96e61c6cd@redhat.com> Date: Mon, 20 Oct 2025 11:38:49 +0200 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 v3] ksm: use range-walk function to jump over holes in scan_get_next_rmap_item To: craftfever , Pedro Demarchi Gomes , Andrew Morton Cc: Xu Xin , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251016012236.4189-1-pedrodemargomes@gmail.com> <844af749-374e-49b3-91f0-a72e951981c8@redhat.com> <6e9ca60a-648c-45e9-9580-27f45a4f2a4d@airmail.cc> 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: <6e9ca60a-648c-45e9-9580-27f45a4f2a4d@airmail.cc> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 18.10.25 09:30, craftfever wrote: > > > David Hildenbrand wrote: >> On 16.10.25 03:22, 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. >>> This problem was previously discussed in [1]. >>> >>> [1] https://lore.kernel.org/linux- >>> mm/423de7a3-1c62-4e72-8e79-19a6413e420c@redhat.com/ >>> >>> --- >> >> This patch does to much in a single patch which makes it >> rather hard to review. >> >> As a first step, we should focus on leaving most of >> scan_get_next_rmap_item() alone and only focus on replacing >> folio_walk by walk_page_range_vma(). >> >> Follow-up cleanups could try cleaning up scan_get_next_rmap_item() >> -- and boy oh boy, does that function scream for quite some cleanups. >> >> This is something minimal based on your v3. I applied plenty of more >> cleanups and I wish we could further shrink the pmd_entry function, >> but I have to give up for today (well, it's already tomorrow :) ). >> >> >> Briefly tested with ksm selftests and my machine did not burn down my >> building. >> >> >> From d971b88056fe3fefe50e5d4fa5b359e8c8331b2c Mon Sep 17 00:00:00 2001 >> From: Pedro Demarchi Gomes >> Date: Wed, 15 Oct 2025 22:22:36 -0300 >> Subject: [PATCH] ksm: use range-walk function to jump over holes in >>  scan_get_next_rmap_item >> >> 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_vma(). The range walker allows KSM to skip over entire >> unmapped holes in a VMA, avoiding unnecessary lookups. >> This problem was previously discussed in [1]. >> >> [1] https://lore.kernel.org/linux- >> mm/423de7a3-1c62-4e72-8e79-19a6413e420c@redhat.com/ >> >> Reported-by: craftfever >> Closes: https://lkml.kernel.org/ >> r/020cf8de6e773bb78ba7614ef250129f11a63781@murena.io >> Signed-off-by: Pedro Demarchi Gomes >> Co-developed-by: David Hildenbrand >> Signed-off-by: David Hildenbrand >> --- >>  mm/ksm.c | 116 ++++++++++++++++++++++++++++++++++++++++++++++++------- >>  1 file changed, 103 insertions(+), 13 deletions(-) >> >> diff --git a/mm/ksm.c b/mm/ksm.c >> index 3aed0478fdcef..8bd2b78c4f869 100644 >> --- a/mm/ksm.c >> +++ b/mm/ksm.c >> @@ -2455,6 +2455,94 @@ static bool should_skip_rmap_item(struct folio >> *folio, >>      return true; >>  } >> >> +struct ksm_next_page_arg { >> +    struct folio *folio; >> +    struct page *page; >> +    unsigned long addr; >> +}; >> + >> +static int ksm_next_page_pmd_entry(pmd_t *pmdp, unsigned long addr, >> unsigned long end, >> +        struct mm_walk *walk) >> +{ >> +    struct ksm_next_page_arg *private = walk->private; >> +    struct vm_area_struct *vma = walk->vma; >> +    pte_t *start_ptep = NULL, *ptep, pte; >> +    struct mm_struct *mm = walk->mm; >> +    struct folio *folio; >> +    struct page *page; >> +    spinlock_t *ptl; >> +    pmd_t pmd; >> + >> +    if (ksm_test_exit(mm)) >> +        return 0; >> +    cond_resched(); >> + >> +    pmd = pmdp_get_lockless(pmdp); >> +    if (!pmd_present(pmd)) >> +        return 0; >> + >> +    if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && pmd_leaf(pmd)) { >> +        ptl = pmd_lock(mm, pmdp); >> +        pmd = pmdp_get(pmdp); >> + >> +        if (!pmd_present(pmd)) { >> +            goto not_found_unlock; >> +        } else if (pmd_leaf(pmd)) { >> +            page = vm_normal_page_pmd(vma, addr, pmd); >> +            if (!page) >> +                goto not_found_unlock; >> +            folio = page_folio(page); >> + >> +            if (folio_is_zone_device(folio) || !folio_test_anon(folio)) >> +                goto not_found_unlock; >> + >> +            page += ((addr & (PMD_SIZE - 1)) >> PAGE_SHIFT); >> +            goto found_unlock; >> +        } >> +        spin_unlock(ptl); >> +    } >> + >> +    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) { >> +        pte = ptep_get(ptep); >> + >> +        if (!pte_present(pte)) >> +            continue; >> + >> +        page = vm_normal_page(vma, addr, pte); >> +        if (!page) >> +            continue; >> +        folio = page_folio(page); >> + >> +        if (folio_is_zone_device(folio) || !folio_test_anon(folio)) >> +            continue; >> +        goto found_unlock; >> +    } >> + >> +not_found_unlock: >> +    spin_unlock(ptl); >> +    if (start_ptep) >> +        pte_unmap(start_ptep); >> +    return 0; >> +found_unlock: >> +    folio_get(folio); >> +    spin_unlock(ptl); >> +    if (start_ptep) >> +        pte_unmap(start_ptep); >> +    private->page = page; >> +    private->folio = folio; >> +    private->addr = addr; >> +    return 1; >> +} >> + >> +static struct mm_walk_ops ksm_next_page_ops = { >> +    .pmd_entry = ksm_next_page_pmd_entry, >> +    .walk_lock = PGWALK_RDLOCK, >> +}; >> + >>  static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) >>  { >>      struct mm_struct *mm; >> @@ -2542,21 +2630,23 @@ static struct ksm_rmap_item >> *scan_get_next_rmap_item(struct page **page) >>              ksm_scan.address = vma->vm_end; >> >>          while (ksm_scan.address < vma->vm_end) { >> +            struct ksm_next_page_arg ksm_next_page_arg; >>              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); >> +            int found; >> + >> +            found = walk_page_range_vma(vma, ksm_scan.address, >> +                            vma->vm_end, >> +                            &ksm_next_page_ops, >> +                            &ksm_next_page_arg); >> + >> +            if (found > 0) { >> +                folio = ksm_next_page_arg.folio; >> +                tmp_page = ksm_next_page_arg.page; >> +                ksm_scan.address = ksm_next_page_arg.addr; >> +            } else { >> +                VM_WARN_ON_ONCE(found < 0); >> +                ksm_scan.address = vma->vm_end - PAGE_SIZE; >>              } >> >>              if (tmp_page) { > > > %) > Guys, I'm so sorry, I"m little confused, can you lease tell further by > e-mail, when patch or couple of patches will be done, so it could > properly tested, 'cause I'm little lost in this progress, is it ready or > not, thank you) In general, we consider code ready once it was reviewed and acked by a maintainer. Andrew usually throws patches ahead of time into mm/mm-unstable while review is still going one. That does not mean yet that the patches will go upstream, it's merely do give them some initial exposure to build bots etc. You can feel free to test the revised patch submitted by me inline, or wait for a v4. -- Cheers David / dhildenb