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[35.187.0.65]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3502b79bdbcsm31255495f8f.23.2024.05.21.02.06.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 May 2024 02:06:24 -0700 (PDT) Date: Tue, 21 May 2024 10:06:20 +0100 From: Vincent Donnefort To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Dan Williams , rostedt@goodmis.org Subject: Re: [PATCH v1 1/2] mm/memory: cleanly support zeropage in vm_insert_page*(), vm_map_pages*() and vmf_insert_mixed() Message-ID: References: <20240430204044.52755-1-david@redhat.com> <20240430204044.52755-2-david@redhat.com> <3decc6c8-9035-44d6-89c6-8d42a5e0bc40@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3decc6c8-9035-44d6-89c6-8d42a5e0bc40@redhat.com> X-Stat-Signature: qbbzjqmf8bsdpcuxc5pxsaqh9w4giqm3 X-Rspamd-Queue-Id: 8EA2140013 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1716282386-457108 X-HE-Meta: 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 LRql9HUW ufjN0ZH5tvRiy51E4HtwLLvexhmIo4H2HNhoCshCrTIVFQZSHShYqb+xhAoyF1vI2d6QtPrh/a81znWFtDcBfbYiWb8bMh/GhB3gIU6kJdWq+sUqENWhkbXAloeSCqJF1v727peCbd/trJxUcjVl0xHgfWnJEu35kXoqBU98FV9mTgt2Rb4jLJk2H8b/uJgs6UxJOdZVAq59lmZ+8EYkcuhOhJac4r6dXOCu7mK/ASh0ov/XAHotfNumUvPSjn2F35f2M5NZyHDrIUYZOEd1Uww573QHfz8R9CB/qeWCZyXNIlmvJ4BOyQZZHSqYKz8eGGPDRPNposEbJZvi+I8XmsYyyeKbB42zzSn6KpR5FJk9XG+LBrfSmvA1ebtlYFOg3yz+H9qgUhXkcDHD2IBx4QlPTdA== 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 Tue, May 21, 2024 at 10:25:43AM +0200, David Hildenbrand wrote: > On 17.05.24 17:07, Vincent Donnefort wrote: > > Hi David, > > > > [...] > > > > > -static int validate_page_before_insert(struct page *page) > > > +static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma) > > > +{ > > > + VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP); > > > + /* > > > + * Whoever wants to forbid the zeropage after some zeropages > > > + * might already have been mapped has to scan the page tables and > > > + * bail out on any zeropages. Zeropages in COW mappings can > > > + * be unshared using FAULT_FLAG_UNSHARE faults. > > > + */ > > > + if (mm_forbids_zeropage(vma->vm_mm)) > > > + return false; > > > + /* zeropages in COW mappings are common and unproblematic. */ > > > + if (is_cow_mapping(vma->vm_flags)) > > > + return true; > > > + /* Mappings that do not allow for writable PTEs are unproblematic. */ > > > + if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) > > > + return false; > > > > Shouldn't we return true here? > > Indeed, thanks! I wish we would have user in the tree already that could > exercise that code path. I have a patch ready to use this path from the memory map tracing! I can either send it once this one is picked-up or you can add it to your series? > > [...] > > > > @@ -2043,7 +2085,7 @@ static int insert_page_in_batch_locked(struct vm_area_struct *vma, pte_t *pte, > > > if (!page_count(page)) > > > return -EINVAL; > > > > This test here prevents inserting the zero-page. > > You mean the existing page_count() check? or the (wrong) vma->vm_flags check > in vm_mixed_zeropage_allowed() ? I meant this page_count() here. As a quick test, I removed that check (also fixed the vm_flags above) and the zero-page was properly mapped! > > -- > Cheers, > > David / dhildenb >