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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 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 X-Stat-Signature: 1rw6kcqdowwwd7zqm3aeirz4nyk4dhwo X-Rspamd-Queue-Id: 7128FA002A X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1723132401-755384 X-HE-Meta: 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 WDIVdr11 UsNzkzZu+VkvlA1aZOqGip7YmziTxK2iTJol97fFuRQGepJU8dv6OaWfs0v/CbluJS4D0/SDIDdLxZwD31h+9hI4nXV1gnm57R+BzsUynDKOZCD6su4oY7F/GtnZYYNVnsQKngwwOs3tFgWNYdOS/6apyKSh74A7cuT20Nf80p/Dumcz49/kG/+qOBh60CTnOPB7QwL/VftmQhuQB9Hr4K26hdcErrvnn/ipopI/3kw/XsIh68Gab5cyja5vU62Tq/vTkIwfDD0Mz2BKm1my4q09yFiUMiTEswyH3uD+iFy03B5peivAQ5y1ld9sZGwJsW6QTuW2BnLjuL+1yweEE5RMTBevy/71bT+qxIhiJ+yKSnsjiVr5KeIevxHYNlQXDB6Ue7oqRPR5p5JX0ry8/veL+7gjm87Xt5pQCCuJhcZWBTAs= 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 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.