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[2003:d8:2f01:5500:ba83:3fd7:6836:62f6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-458705ce685sm26933245e9.30.2025.07.24.10.57.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Jul 2025 10:57:23 -0700 (PDT) Message-ID: <0a70058f-e2fa-4f83-ace5-f58df589ac46@redhat.com> Date: Thu, 24 Jul 2025 19:57:22 +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 v4 2/3] khugepaged: Optimize __collapse_huge_page_copy_succeeded() by PTE batching To: Lorenzo Stoakes , Dev Jain Cc: akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250724052301.23844-1-dev.jain@arm.com> <20250724052301.23844-3-dev.jain@arm.com> <83c00fa9-37a3-4024-b3d1-20e7749b06c9@lucifer.local> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >> + if (folio_test_large(src)) { >> + unsigned int max_nr_ptes = (end - address) >> PAGE_SHIFT; >> + >> + nr_ptes = folio_pte_batch(src, _pte, pteval, max_nr_ptes); >> + } else { >> release_pte_folio(src); >> + } >> + >> /* >> * ptl mostly unnecessary, but preempt has to >> * be disabled to update the per-cpu stats >> * inside folio_remove_rmap_pte(). >> */ >> spin_lock(ptl); >> - ptep_clear(vma->vm_mm, address, _pte); >> - folio_remove_rmap_pte(src, src_page, vma); >> + clear_ptes(vma->vm_mm, address, _pte, nr_ptes); >> + folio_remove_rmap_ptes(src, src_page, nr_ptes, vma); >> spin_unlock(ptl); >> - free_folio_and_swap_cache(src); >> + free_swap_cache(src); >> + folio_put_refs(src, nr_ptes); > > Hm one thing here though is the free_folio_and_swap_cache() does: > > free_swap_cache(folio); > if (!is_huge_zero_folio(folio)) > folio_put(folio); > > Whereas here you unconditionally reduce the reference count. Might this > cause issues with the shrinker version of the huge zero folio? > > Should this be: > > if (!is_huge_zero_folio(src)) > folio_put_refs(src, nr_ptes); > > Or do we otherwise avoid issues with this? (resending my reply) The huge zero folio is never PTE-mapped. -- Cheers, David / dhildenb