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 992FE6B0279 for ; Mon, 22 May 2017 16:19:31 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id d142so173267312oib.7 for ; Mon, 22 May 2017 13:19:31 -0700 (PDT) Received: from mail-oi0-x22f.google.com (mail-oi0-x22f.google.com. [2607:f8b0:4003:c06::22f]) by mx.google.com with ESMTPS id q3si7826236oig.301.2017.05.22.13.19.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 May 2017 13:19:30 -0700 (PDT) Received: by mail-oi0-x22f.google.com with SMTP id h4so176108213oib.3 for ; Mon, 22 May 2017 13:19:30 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20170522201416.GA8168@redhat.com> References: <20170522165206.6284-1-jglisse@redhat.com> <20170522165206.6284-9-jglisse@redhat.com> <20170522201416.GA8168@redhat.com> From: Dan Williams Date: Mon, 22 May 2017 13:19:29 -0700 Message-ID: Subject: Re: [HMM 08/15] mm/ZONE_DEVICE: special case put_page() for device private pages Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: Andrew Morton , "linux-kernel@vger.kernel.org" , Linux MM , John Hubbard , David Nellans , "Kirill A . Shutemov" , Ross Zwisler On Mon, May 22, 2017 at 1:14 PM, Jerome Glisse wrote: > On Mon, May 22, 2017 at 12:29:53PM -0700, Dan Williams wrote: >> On Mon, May 22, 2017 at 9:51 AM, J=C3=A9r=C3=B4me Glisse wrote: >> > A ZONE_DEVICE page that reach a refcount of 1 is free ie no longer >> > have any user. For device private pages this is important to catch >> > and thus we need to special case put_page() for this. >> > >> > Signed-off-by: J=C3=A9r=C3=B4me Glisse >> > Cc: Kirill A. Shutemov >> > Cc: Dan Williams >> > Cc: Ross Zwisler >> > --- >> > include/linux/mm.h | 30 ++++++++++++++++++++++++++++++ >> > kernel/memremap.c | 1 - >> > 2 files changed, 30 insertions(+), 1 deletion(-) >> > >> > diff --git a/include/linux/mm.h b/include/linux/mm.h >> > index a825dab..11f7bac 100644 >> > --- a/include/linux/mm.h >> > +++ b/include/linux/mm.h >> > @@ -23,6 +23,7 @@ >> > #include >> > #include >> > #include >> > +#include >> > >> > struct mempolicy; >> > struct anon_vma; >> > @@ -795,6 +796,20 @@ static inline bool is_device_private_page(const s= truct page *page) >> > return ((page_zonenum(page) =3D=3D ZONE_DEVICE) && >> > (page->pgmap->type =3D=3D MEMORY_DEVICE_PRIVATE)); >> > } >> > + >> > +static inline void put_zone_device_private_page(struct page *page) >> > +{ >> > + int count =3D page_ref_dec_return(page); >> > + >> > + /* >> > + * If refcount is 1 then page is freed and refcount is stable = as nobody >> > + * holds a reference on the page. >> > + */ >> > + if (count =3D=3D 1) >> > + page->pgmap->page_free(page, page->pgmap->data); >> > + else if (!count) >> > + __put_page(page); >> > +} >> > #else >> > static inline bool is_zone_device_page(const struct page *page) >> > { >> > @@ -805,6 +820,10 @@ static inline bool is_device_private_page(const s= truct page *page) >> > { >> > return false; >> > } >> > + >> > +static inline void put_zone_device_private_page(struct page *page) >> > +{ >> > +} >> > #endif >> > >> > static inline void get_page(struct page *page) >> > @@ -822,6 +841,17 @@ static inline void put_page(struct page *page) >> > { >> > page =3D compound_head(page); >> > >> > + /* >> > + * For private device pages we need to catch refcount transiti= on from >> > + * 2 to 1, when refcount reach one it means the private device= page is >> > + * free and we need to inform the device driver through callba= ck. See >> > + * include/linux/memremap.h and HMM for details. >> > + */ >> > + if (unlikely(is_device_private_page(page))) { >> >> Since I presume HMM is a niche use case can we make this a >> "static_branch_unlikely(&hmm_key) && is_device_private_page(page))"? >> That way non-hmm platforms see minimal overhead. > > Like i said in the cover letter i am bit anxious about doing for I don't think you copied me on the cover letter. > an inline function. I don't see any existing case for inline > function and static key. Is that suppose to work ? > > How widespread HMM use will be is hard to guess. Usual chicken > and egg plus adoption thing. If GPGPU compte keeps growing and > it seems it does then HMM likely gonna be enable and actively > use for large chunk of those computer that have GPGPU workload. > > I will test a static key of that branch and see if it explodes > because put_page() is an inline function. memcpy_mcsafe() is an existing example of a static inline with a static branch. Hasn't seemed to have caused any problems to date. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org