From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 40840CAC5A5 for ; Fri, 19 Sep 2025 08:14:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Dc53JcOzdrcUIu2iVuDKY0KAeJ//x1/I8rOfO8TAJ0E=; b=QJlzRVrs283yNhhG2VYKnIsdRL J6QtZ5yQn+yP8K5NL9KKqUnJw9VzEl9+1woazCLciqyGdNXNBgrO/eEKev5IMKrRfzj3k0sXL02mA IfAixQQOTMo7VN0Z8I+bZTFfjyzV/9K4RjdOfKZ6qySaSGovZ8YJQd6pmZmFUzsKoKPC4jT8AoS1M fDVsgwzLfYxn7cMcQb4YoUqYskqoHgMhps5qR68O03kh1Jac7K8yEzXJfyB9y/839V++/T/6zulNn 4NlgrRZXJJcUxoP9FMLNLxRRSNK02DgGmAACFZj8nnFGdAGcwCcq9x2PXdlcqiHcbvkIDDV0Z1FyI XovryGmA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uzWGN-00000002DSw-1lcR; Fri, 19 Sep 2025 08:14:39 +0000 Received: from out-174.mta0.migadu.com ([2001:41d0:1004:224b::ae]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uzWGL-00000002DS6-1I5z for linux-mediatek@lists.infradead.org; Fri, 19 Sep 2025 08:14:38 +0000 Message-ID: <4cf41cd5-e93a-412b-b209-4180bd2d4015@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758269664; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Dc53JcOzdrcUIu2iVuDKY0KAeJ//x1/I8rOfO8TAJ0E=; b=BmeGBByUETlTGTM2SzKN9sT+aElM0iDnr9NVCQ0Y4S5LyZS5qVFjUY0/ZQhQcjxmkujkwF lcqoAIrEgGu+qx5juQO8M0lGpLChTPtWmm4PXKC8zXPXthowkvLtjPKwUnGPeV4fEL7kE5 GoVQEabwufMTPdzDfKN5emTG80lC0C8= Date: Fri, 19 Sep 2025 16:14:11 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v5 2/6] mm: remap unused subpages to shared zeropage when splitting isolated thp Content-Language: en-US To: David Hildenbrand Cc: =?UTF-8?B?UXVuLXdlaSBMaW4gKOael+e+pOW0tCk=?= , "catalin.marinas@arm.com" , "usamaarif642@gmail.com" , "linux-mm@kvack.org" , "yuzhao@google.com" , "akpm@linux-foundation.org" , "corbet@lwn.net" , =?UTF-8?B?QW5kcmV3IFlhbmcgKOaliuaZuuW8tyk=?= , "npache@redhat.com" , "rppt@kernel.org" , "willy@infradead.org" , "kernel-team@meta.com" , "roman.gushchin@linux.dev" , "hannes@cmpxchg.org" , "cerasuolodomenico@gmail.com" , "linux-kernel@vger.kernel.org" , "ryncsn@gmail.com" , "surenb@google.com" , "riel@surriel.com" , "shakeel.butt@linux.dev" , =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , "linux-doc@vger.kernel.org" , =?UTF-8?B?Q2FzcGVyIExpICjmnY7kuK3mpq4p?= , "ryan.roberts@arm.com" , "linux-mediatek@lists.infradead.org" , "baohua@kernel.org" , "kaleshsingh@google.com" , "zhais@google.com" , "linux-arm-kernel@lists.infradead.org" References: <20240830100438.3623486-1-usamaarif642@gmail.com> <20240830100438.3623486-3-usamaarif642@gmail.com> <434c092b-0f19-47bf-a5fa-ea5b4b36c35e@redhat.com> <120445c8-7250-42e0-ad6a-978020c8fad3@linux.dev> <9d2c3e3e-439d-4695-b7c9-21fa52f48ced@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <9d2c3e3e-439d-4695-b7c9-21fa52f48ced@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250919_011437_487708_CF675042 X-CRM114-Status: GOOD ( 28.92 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On 2025/9/19 15:55, David Hildenbrand wrote: >>> I think where possible we really only want to identify problematic >>> (tagged) pages and skip them. And we should either look into fixing KSM >>> as well or finding out why KSM is not affected. >> >> Yeah. Seems like we could introduce a new helper, >> folio_test_mte_tagged(struct >> folio *folio). By default, it would return false, and architectures like >> arm64 >> can override it. > > If we add a new helper it should instead express the semantics that we > cannot deduplicate. Agreed. > > For THP, I recall that only some pages might be tagged. So likely we > want to check per page. Yes, a per-page check would be simpler. > >> >> Looking at the code, the PG_mte_tagged flag is not set for regular THP. > > I think it's supported for THP per page. Only for hugetlb we tag the > whole thing through the head page instead of individual pages. Right. That's exactly what I meant. > >> The MTE >> status actually comes from the VM_MTE flag in the VMA that maps it. >> > > During the rmap walk we could check the VMA flag, but there would be no > way to just stop the THP shrinker scanning this page early. > >> static inline bool folio_test_hugetlb_mte_tagged(struct folio *folio) >> { >>     bool ret = test_bit(PG_mte_tagged, &folio->flags.f); >> >>     VM_WARN_ON_ONCE(!folio_test_hugetlb(folio)); >> >>     /* >>      * If the folio is tagged, ensure ordering with a likely subsequent >>      * read of the tags. >>      */ >>     if (ret) >>         smp_rmb(); >>     return ret; >> } >> >> static inline bool page_mte_tagged(struct page *page) >> { >>     bool ret = test_bit(PG_mte_tagged, &page->flags.f); >> >>     VM_WARN_ON_ONCE(folio_test_hugetlb(page_folio(page))); >> >>     /* >>      * If the page is tagged, ensure ordering with a likely subsequent >>      * read of the tags. >>      */ >>     if (ret) >>         smp_rmb(); >>     return ret; >> } >> >> contpte_set_ptes() >>     __set_ptes() >>         __set_ptes_anysz() >>             __sync_cache_and_tags() >>                 mte_sync_tags() >>                     set_page_mte_tagged() >> >> Then, having the THP shrinker skip any folios that are identified as >> MTE-tagged. > > Likely we should just do something like (maybe we want better naming) > > #ifndef page_is_mergable > #define page_is_mergable(page) (true) > #endif Maybe something like page_is_optimizable()? Just a thought ;p > > And for arm64 have it be > > #define page_is_mergable(page) (!page_mte_tagged(page)) > > > And then do > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 1f0813b956436..1cac9093918d6 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -4251,7 +4251,8 @@ static bool thp_underused(struct folio *folio) > >         for (i = 0; i < folio_nr_pages(folio); i++) { >                 kaddr = kmap_local_folio(folio, i * PAGE_SIZE); > -               if (!memchr_inv(kaddr, 0, PAGE_SIZE)) { > +               if (page_is_mergable(folio_page(folio, i)) && > +                   !memchr_inv(kaddr, 0, PAGE_SIZE)) { >                         num_zero_pages++; >                         if (num_zero_pages > khugepaged_max_ptes_none) { >                                 kunmap_local(kaddr); > diff --git a/mm/migrate.c b/mm/migrate.c > index 946253c398072..476a9a9091bd3 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -306,6 +306,8 @@ static bool try_to_map_unused_to_zeropage(struct > page_vma_mapped_walk *pvmw, > >         if (PageCompound(page)) >                 return false; > +       if (!page_is_mergable(page)) > +               return false; >         VM_BUG_ON_PAGE(!PageAnon(page), page); >         VM_BUG_ON_PAGE(!PageLocked(page), page); >         VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page); Looks good to me! > > > For KSM, similarly just bail out early. But still wondering if this is > already checked > somehow for KSM. +1 I'm looking for a machine to test it on.