From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id 186F12806EE for ; Fri, 19 May 2017 12:31:17 -0400 (EDT) Received: by mail-pg0-f71.google.com with SMTP id d127so63111289pga.11 for ; Fri, 19 May 2017 09:31:17 -0700 (PDT) Received: from NAM03-DM3-obe.outbound.protection.outlook.com (mail-dm3nam03on0118.outbound.protection.outlook.com. [104.47.41.118]) by mx.google.com with ESMTPS id j13si9123913pgn.258.2017.05.19.09.31.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 19 May 2017 09:31:15 -0700 (PDT) From: "Zi Yan" Subject: Re: [PATCH v5 01/11] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 1 Date: Fri, 19 May 2017 12:31:08 -0400 Message-ID: <07441274-3C64-4376-8225-39CD052399B4@cs.rutgers.edu> In-Reply-To: <76a36bee-0f1c-a2f4-6f5c-78394ac46ee4@intel.com> References: <20170420204752.79703-1-zi.yan@sent.com> <20170420204752.79703-2-zi.yan@sent.com> <76a36bee-0f1c-a2f4-6f5c-78394ac46ee4@intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=_MailMate_3756686B-DFCA-40C3-9666-A90C788D8246_="; micalg=pgp-sha512; protocol="application/pgp-signature" Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: n-horiguchi@ah.jp.nec.com, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, minchan@kernel.org, vbabka@suse.cz, mgorman@techsingularity.net, mhocko@kernel.org, khandual@linux.vnet.ibm.com, dnellans@nvidia.com This is an OpenPGP/MIME signed message (RFC 3156 and 4880). --=_MailMate_3756686B-DFCA-40C3-9666-A90C788D8246_= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On 19 May 2017, at 11:55, Dave Hansen wrote: > On 04/20/2017 01:47 PM, Zi Yan wrote: >> pmd_present() checks _PAGE_PSE along with _PAGE_PRESENT to avoid >> false negative return when it races with thp spilt >> (during which _PAGE_PRESENT is temporary cleared.) I don't think that >> dropping _PAGE_PSE check in pmd_present() works well because it can >> hurt optimization of tlb handling in thp split. >> In the current kernel, bits 1-4 are not used in non-present format >> since commit 00839ee3b299 ("x86/mm: Move swap offset/type up in PTE to= >> work around erratum"). So let's move _PAGE_SWP_SOFT_DIRTY to bit 1. >> Bit 7 is used as reserved (always clear), so please don't use it for >> other purpose. > > This description lacks a problem statement. What's the problem? > > _PAGE_PSE is used to distinguish between a truly non-present > (_PAGE_PRESENT=3D0) PMD, and a PMD which is undergoing a THP > split and should be treated as present. > > But _PAGE_SWP_SOFT_DIRTY currently uses the _PAGE_PSE bit, > which would cause confusion between one of those PMDs > undergoing a THP split, and a soft-dirty PMD. > > Thus, we need to move the bit. > > Does that capture it? Yes. I will add this in the next version. > >> Signed-off-by: Naoya Horiguchi >> Signed-off-by: Zi Yan >> --- >> arch/x86/include/asm/pgtable_64.h | 12 +++++++++--- >> arch/x86/include/asm/pgtable_types.h | 10 +++++----- >> 2 files changed, 14 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/= pgtable_64.h >> index 73c7ccc38912..770b5ae271ed 100644 >> --- a/arch/x86/include/asm/pgtable_64.h >> +++ b/arch/x86/include/asm/pgtable_64.h >> @@ -157,15 +157,21 @@ static inline int pgd_large(pgd_t pgd) { return = 0; } >> /* >> * Encode and de-code a swap entry >> * >> - * | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0| <- bit numb= er >> - * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| <- bit name= s >> - * | OFFSET (14->63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0| <- swp entr= y >> + * | ... | 11| 10| 9|8|7|6|5| 4| 3|2| 1|0| <- bit num= ber >> + * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit nam= es >> + * | OFFSET (14->63) | TYPE (9-13) |0|0|X|X| X| X|X|SD|0| <- swp ent= ry > > So, this diagram was incomplete before? It should have had "SD" under > bit 7 for swap entries? Right. SD bit is used only when CONFIG_MEM_SOFT_DIRTY is enabled, but it = is good to mark it in the diagram to avoid conflicts. > >> * G (8) is aliased and used as a PROT_NONE indicator for >> * !present ptes. We need to start storing swap entries above >> * there. We also need to avoid using A and D because of an >> * erratum where they can be incorrectly set by hardware on >> * non-present PTEs. >> + * >> + * SD (1) in swp entry is used to store soft dirty bit, which helps u= s >> + * remember soft dirty over page migration >> + * >> + * Bit 7 in swp entry should be 0 because pmd_present checks not only= P, >> + * but also L and G. >> */ -- Best Regards Yan Zi --=_MailMate_3756686B-DFCA-40C3-9666-A90C788D8246_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQEcBAEBCgAGBQJZHx3MAAoJEEGLLxGcTqbMY8oH/i5aUg+WqqwKxedY35B5iNk8 ksoYhtA2H3cGNtiSbpGwzKyEnk9/vTOWfp2ipIyGRv8jBakh49BYwL+islthYVgw 38V69YGpumbxOjnO4vnc9FNTcWwO3280LNtvWa8vWz5JZEifoCujNLTBQycZmVNg ZkGaDEHHRJmkCPxUQKADFT34l/HB6/u9LccXknXikLOMP5PcthwCsHJYd3devp8i AC+jmMNyz0TXskZ/d0ngimzYzz6BHLIKvw4Fqb16P2bxPLV4g6NoISDsDI7Sdpip emkShiiKvRdQEk2koCUuEmZF8ozzu3ZTkQXdyWrYQfy4hBhDgflTaP9H9kCSIx8= =CNSM -----END PGP SIGNATURE----- --=_MailMate_3756686B-DFCA-40C3-9666-A90C788D8246_=-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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