From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 5B40C6B0387 for ; Thu, 9 Feb 2017 10:08:05 -0500 (EST) Received: by mail-oi0-f72.google.com with SMTP id y140so6180174oie.2 for ; Thu, 09 Feb 2017 07:08:05 -0800 (PST) Received: from NAM01-SN1-obe.outbound.protection.outlook.com (mail-sn1nam01on0106.outbound.protection.outlook.com. [104.47.32.106]) by mx.google.com with ESMTPS id n187si4742265oih.239.2017.02.09.07.08.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 09 Feb 2017 07:08:04 -0800 (PST) From: Zi Yan Subject: Re: [PATCH v3 04/14] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 1 Date: Thu, 9 Feb 2017 09:07:56 -0600 Message-ID: In-Reply-To: <20170209091458.GA15649@hori1.linux.bs1.fc.nec.co.jp> References: <20170205161252.85004-1-zi.yan@sent.com> <20170205161252.85004-5-zi.yan@sent.com> <20170209091458.GA15649@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=_MailMate_A5B4B13E-8536-4F97-B856-4812B7FBFA18_="; micalg=pgp-sha512; protocol="application/pgp-signature" Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "kirill.shutemov@linux.intel.com" , "akpm@linux-foundation.org" , "minchan@kernel.org" , "vbabka@suse.cz" , "mgorman@techsingularity.net" , "khandual@linux.vnet.ibm.com" --=_MailMate_A5B4B13E-8536-4F97-B856-4812B7FBFA18_= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On 9 Feb 2017, at 3:14, Naoya Horiguchi wrote: > On Sun, Feb 05, 2017 at 11:12:42AM -0500, Zi Yan wrote: >> From: Naoya Horiguchi >> >> 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. >> >> Signed-off-by: Naoya Horiguchi >> >> ChangeLog v3: >> - Move _PAGE_SWP_SOFT_DIRTY to bit 1, it was placed at bit 6. Because >> some CPUs might accidentally set bit 5 or 6. >> >> Signed-off-by: Zi Yan >> --- > > More documenting will be helpful, could you do like follows? Sure. Thanks for helping. > > Thanks, > Naoya Horiguchi > --- > From: Naoya Horiguchi > Date: Sun, 5 Feb 2017 11:12:42 -0500 > Subject: [PATCH] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 1= > > 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. > > 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/p= gtable_64.h > index 73c7ccc38912..07c98c85cc96 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 numbe= r > - * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| <- bit names= > - * | OFFSET (14->63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0| <- swp 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|0|X|X| X| X|X|SD|0| <- swp entr= y > * > * 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 us= > + * remember soft dirty over page migration. > + * > + * Bit 7 in swp entry should be 0 because pmd_present checks not only = P, > + * but G. > */ > #define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) > #define SWP_TYPE_BITS 5 > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/as= m/pgtable_types.h > index 8b4de22d6429..3695abd58ef6 100644 > --- a/arch/x86/include/asm/pgtable_types.h > +++ b/arch/x86/include/asm/pgtable_types.h > @@ -97,15 +97,15 @@ > /* > * Tracking soft dirty bit when a page goes to a swap is tricky. > * We need a bit which can be stored in pte _and_ not conflict > - * with swap entry format. On x86 bits 6 and 7 are *not* involved > - * into swap entry computation, but bit 6 is used for nonlinear > - * file mapping, so we borrow bit 7 for soft dirty tracking. > + * with swap entry format. On x86 bits 1-4 are *not* involved > + * into swap entry computation, but bit 7 is used for thp migration, > + * so we borrow bit 1 for soft dirty tracking. > * > * Please note that this bit must be treated as swap dirty page > - * mark if and only if the PTE has present bit clear! > + * mark if and only if the PTE/PMD has present bit clear! > */ > #ifdef CONFIG_MEM_SOFT_DIRTY > -#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE > +#define _PAGE_SWP_SOFT_DIRTY _PAGE_RW > #else > #define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) > #endif > -- = > 2.7.4 -- Best Regards Yan Zi --=_MailMate_A5B4B13E-8536-4F97-B856-4812B7FBFA18_= 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 iQEcBAEBCgAGBQJYnIXMAAoJEEGLLxGcTqbMCvoH/3Q4pBypQF0iKmapJ0dHlavV euz08mB8HaBtSkRIrYl7zlaDBDesM1nm07gYXZHOFwBBRSljWf+Osy557y0f29Pu NyLHMgDahTT95U2SOfSyD+LArdP9rTLl9djsBUKDrzGaM+ljIGFia3WLN563KqRq PczDNB49VhPRc/bsQaA39an8OK9hd0k7uXS2O7b61N5omXqGgaJ43lzxaynhpaZ8 IANA22IRSF21tltJlj3iqL2Wa9UwMrbxF0uM8l/heS0QzC/Psc5UnHidm5w7gXLY rMiPeNe+9VQJBy4lNBq3GoPjDELm8crCLi1B8N2G4o4JpkkhGN0dIiwrJYEnqSY= =HqSG -----END PGP SIGNATURE----- --=_MailMate_A5B4B13E-8536-4F97-B856-4812B7FBFA18_=-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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