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([2620:10d:c092:500::7:3531]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5bbb2c3c991sm756035a12.35.2024.08.08.08.53.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Aug 2024 08:53:18 -0700 (PDT) Message-ID: Date: Thu, 8 Aug 2024 16:53:17 +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 v2 2/4] mm: remap unused subpages to shared zeropage when splitting isolated thp To: Johannes Weiner Cc: akpm@linux-foundation.org, linux-mm@kvack.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, yuzhao@google.com, david@redhat.com, baohua@kernel.org, ryan.roberts@arm.com, rppt@kernel.org, willy@infradead.org, cerasuolodomenico@gmail.com, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com, Shuang Zhai References: <20240807134732.3292797-1-usamaarif642@gmail.com> <20240807134732.3292797-3-usamaarif642@gmail.com> <20240807200241.GB1828817@cmpxchg.org> Content-Language: en-US From: Usama Arif In-Reply-To: <20240807200241.GB1828817@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 07/08/2024 21:02, Johannes Weiner wrote: > On Wed, Aug 07, 2024 at 02:46:47PM +0100, Usama Arif wrote: >> @@ -177,13 +177,56 @@ void putback_movable_pages(struct list_head *l) >> } >> } >> >> +static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, >> + struct folio *folio, >> + unsigned long idx) >> +{ >> + struct page *page = folio_page(folio, idx); >> + bool contains_data; >> + pte_t newpte; >> + void *addr; >> + >> + VM_BUG_ON_PAGE(PageCompound(page), page); >> + VM_BUG_ON_PAGE(!PageAnon(page), page); >> + VM_BUG_ON_PAGE(!PageLocked(page), page); >> + VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page); >> + >> + if (PageMlocked(page) || (pvmw->vma->vm_flags & VM_LOCKED)) >> + return false; >> + >> + /* >> + * The pmd entry mapping the old thp was flushed and the pte mapping >> + * this subpage has been non present. If the subpage is only zero-filled >> + * then map it to the shared zeropage. >> + */ >> + addr = kmap_local_page(page); >> + contains_data = memchr_inv(addr, 0, PAGE_SIZE); >> + kunmap_local(addr); >> + >> + if (contains_data || mm_forbids_zeropage(pvmw->vma->vm_mm)) >> + return false; >> + >> + newpte = pte_mkspecial(pfn_pte(page_to_pfn(ZERO_PAGE(pvmw->address)), >> + pvmw->vma->vm_page_prot)); > > Why not use my_zero_pfn() here? On many configurations this just > returns zero_pfn and avoids the indirection through mem_map. > >> @@ -904,7 +958,7 @@ static int writeout(struct address_space *mapping, struct folio *folio) >> * At this point we know that the migration attempt cannot >> * be successful. >> */ >> - remove_migration_ptes(folio, folio, false); >> + remove_migration_ptes(folio, folio, false, false); > > bool params are not great for callsite readability. > > How about a flags parameter and using names? > > enum rmp_flags { > RMP_LOCKED = 1 << 0, > RMP_ZEROPAGES = 1 << 1, > } Thanks! Will include both of the above changes in the next revision.