From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 646F16B027B for ; Wed, 17 Oct 2018 04:47:47 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id e49-v6so12227283edd.20 for ; Wed, 17 Oct 2018 01:47:47 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id w1-v6si8378100edh.16.2018.10.17.01.47.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Oct 2018 01:47:46 -0700 (PDT) Date: Wed, 17 Oct 2018 10:47:44 +0200 From: Michal Hocko Subject: Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Message-ID: <20181017084744.GH18839@dhcp22.suse.cz> References: <20181015202456.2171.88406.stgit@localhost.localdomain> <20181015202656.2171.92963.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181015202656.2171.92963.stgit@localhost.localdomain> Sender: owner-linux-mm@kvack.org List-ID: To: Alexander Duyck Cc: linux-mm@kvack.org, akpm@linux-foundation.org, pavel.tatashin@microsoft.com, dave.jiang@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, davem@davemloft.net, yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, vbabka@suse.cz, sparclinux@vger.kernel.org, dan.j.williams@intel.com, ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net, mingo@kernel.org, kirill.shutemov@linux.intel.com On Mon 15-10-18 13:26:56, Alexander Duyck wrote: > This change makes it so that we use the same approach that was already in > use on Sparc on all the archtectures that support a 64b long. > > This is mostly motivated by the fact that 8 to 10 store/move instructions > are likely always going to be faster than having to call into a function > that is not specialized for handling page init. > > An added advantage to doing it this way is that the compiler can get away > with combining writes in the __init_single_page call. As a result the > memset call will be reduced to only about 4 write operations, or at least > that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and > count/mapcount seem to be cancelling out at least 4 of the 8 assignments on > my system. > > One change I had to make to the function was to reduce the minimum page > size to 56 to support some powerpc64 configurations. This really begs for numbers. I do not mind the change itself with some minor comments below. [...] > diff --git a/include/linux/mm.h b/include/linux/mm.h > index bb0de406f8e7..ec6e57a0c14e 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { } > * zeroing by defining this macro in . > */ > #ifndef mm_zero_struct_page Do we still need this ifdef? I guess we can wait for an arch which doesn't like this change and then add the override. I would rather go simple if possible. > +#if BITS_PER_LONG == 64 > +/* This function must be updated when the size of struct page grows above 80 > + * or reduces below 64. The idea that compiler optimizes out switch() > + * statement, and only leaves move/store instructions > + */ > +#define mm_zero_struct_page(pp) __mm_zero_struct_page(pp) > +static inline void __mm_zero_struct_page(struct page *page) > +{ > + unsigned long *_pp = (void *)page; > + > + /* Check that struct page is either 56, 64, 72, or 80 bytes */ > + BUILD_BUG_ON(sizeof(struct page) & 7); > + BUILD_BUG_ON(sizeof(struct page) < 56); > + BUILD_BUG_ON(sizeof(struct page) > 80); > + > + switch (sizeof(struct page)) { > + case 80: > + _pp[9] = 0; /* fallthrough */ > + case 72: > + _pp[8] = 0; /* fallthrough */ > + default: > + _pp[7] = 0; /* fallthrough */ > + case 56: > + _pp[6] = 0; > + _pp[5] = 0; > + _pp[4] = 0; > + _pp[3] = 0; > + _pp[2] = 0; > + _pp[1] = 0; > + _pp[0] = 0; > + } This just hit my eyes. I have to confess I have never seen default: to be not the last one in the switch. Can we have case 64 instead or does gcc complain? I would be surprised with the set of BUILD_BUG_ONs. > +} > +#else > #define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page))) > #endif > +#endif > > /* > * Default maximum number of active map areas, this limits the number of vmas > -- Michal Hocko SUSE Labs