From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx187.postini.com [74.125.245.187]) by kanga.kvack.org (Postfix) with SMTP id 343CF6B004D for ; Thu, 5 Jan 2012 11:29:11 -0500 (EST) Message-ID: <4F05CFAF.9020502@ah.jp.nec.com> Date: Thu, 05 Jan 2012 11:28:31 -0500 From: Naoya Horiguchi MIME-Version: 1.0 Subject: Re: [PATCH 1/4] pagemap: avoid splitting thp when reading /proc/pid/pagemap References: <1324506228-18327-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1324506228-18327-2-git-send-email-n-horiguchi@ah.jp.nec.com> <20120104155042.c24e529b.akpm@linux-foundation.org> In-Reply-To: <20120104155042.c24e529b.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Naoya Horiguchi , linux-mm@kvack.org, David Rientjes , Andi Kleen , Wu Fengguang , Andrea Arcangeli , KOSAKI Motohiro , KAMEZAWA Hiroyuki , linux-kernel@vger.kernel.org On Wed, Jan 04, 2012 at 03:50:42PM -0800, Andrew Morton wrote: > On Wed, 21 Dec 2011 17:23:45 -0500 > Naoya Horiguchi wrote: > > > Thp split is not necessary if we explicitly check whether pmds are > > mapping thps or not. This patch introduces the check and the code > > to generate pagemap entries for pmds mapping thps, which results in > > less performance impact of pagemap on thp. > > > > > > ... > > The type choices seem odd: > > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > +static u64 thp_pte_to_pagemap_entry(pte_t pte, int offset) > > +{ > > + u64 pme = 0; > > Why are these u64? I guess (I just copied this type choice from other *pte_to_pagemap_entry() type functions) it's because each entry in /proc/pid/pagemap is in fixed sized (64 bit) format as described in the comment above pagemap_read(). > Should we have a pme_t, matching pte_t, pmd_t, etc? Yes, it makes code's meaning clearer. > > > + if (pte_present(pte)) > > + pme = PM_PFRAME(pte_pfn(pte) + offset) > > + | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT; > > + return pme; > > +} > > +#else > > +static inline u64 thp_pte_to_pagemap_entry(pte_t pte, int offset) > > +{ > > + return 0; > > +} > > +#endif > > + > > static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > struct mm_walk *walk) > > { > > @@ -665,14 +684,34 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > > struct pagemapread *pm = walk->private; > > pte_t *pte; > > int err = 0; > > - > > - split_huge_page_pmd(walk->mm, pmd); > > + u64 pfn = PM_NOT_PRESENT; > > Again, why a u64? pfn's are usually unsigned long. I think variable's name 'pfn' is wrong rather than type choice because this variable stores pagemap entry which is not a pure pfn. There's room for improvement, so I'll try it in the next turn. Thanks, Naoya -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org