From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id F38216B0037 for ; Fri, 1 Aug 2014 01:03:37 -0400 (EDT) Received: by mail-pd0-f175.google.com with SMTP id r10so4822854pdi.20 for ; Thu, 31 Jul 2014 22:03:37 -0700 (PDT) Received: from mail-pa0-x236.google.com (mail-pa0-x236.google.com [2607:f8b0:400e:c03::236]) by mx.google.com with ESMTPS id qm2si25283pac.149.2014.07.31.22.03.36 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 31 Jul 2014 22:03:37 -0700 (PDT) Received: by mail-pa0-f54.google.com with SMTP id fa1so5004790pad.41 for ; Thu, 31 Jul 2014 22:03:36 -0700 (PDT) Date: Thu, 31 Jul 2014 22:01:56 -0700 (PDT) From: Hugh Dickins Subject: Re: [PATCH 2/5] mm, shmem: Add shmem_locate function In-Reply-To: <1406036632-26552-3-git-send-email-jmarchan@redhat.com> Message-ID: References: <1406036632-26552-1-git-send-email-jmarchan@redhat.com> <1406036632-26552-3-git-send-email-jmarchan@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Marchand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-doc@vger.kernel.org, Hugh Dickins , Arnaldo Carvalho de Melo , Ingo Molnar , Paul Mackerras , Peter Zijlstra , linux390@de.ibm.com, Heiko Carstens , Martin Schwidefsky , Randy Dunlap On Tue, 22 Jul 2014, Jerome Marchand wrote: > The shmem subsytem is kind of a black box: the generic mm code can't I'm happier with that black box than you are :) > always know where a specific page physically is. This patch adds the > shmem_locate() function to find out the physical location of shmem > pages (resident, in swap or swapcache). If the optional argument count > isn't NULL and the page is resident, it also returns the mapcount value > of this page. > This is intended to allow finer accounting of shmem/tmpfs pages. > > Signed-off-by: Jerome Marchand > --- > include/linux/mm.h | 7 +++++++ > mm/shmem.c | 29 +++++++++++++++++++++++++++++ > 2 files changed, 36 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index e69ee9d..34099fa 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1066,6 +1066,13 @@ extern bool skip_free_areas_node(unsigned int flags, int nid); > > int shmem_zero_setup(struct vm_area_struct *); > #ifdef CONFIG_SHMEM > + > +#define SHMEM_NOTPRESENT 1 /* page is not present in memory */ > +#define SHMEM_RESIDENT 2 /* page is resident in RAM */ > +#define SHMEM_SWAPCACHE 3 /* page is in swap cache */ > +#define SHMEM_SWAP 4 /* page is paged out */ > + > +extern int shmem_locate(struct vm_area_struct *vma, pgoff_t pgoff, int *count); Please place these, or what's needed of them, in include/linux/shmem_fs.h, rather than in the very overloaded include/linux/mm.h. You will need a !CONFIG_SHMEM stub for shmem_locate(), or whatever it ends up being called. > bool shmem_mapping(struct address_space *mapping); Oh, you're following a precedent, that's already bad placement. And it (but not its !CONFIG_SHMEM stub) is duplicated in shmem_fs.h. Perhaps because we were moving shmem_zero_setup() from mm.h to shmem_fs.h some time ago, but never got around to cleaning up the old location. Well, please place the new ones in shmem_fs.h, and I ought to clean up the rest at a time which does not interfere with you. > #else > static inline bool shmem_mapping(struct address_space *mapping) > diff --git a/mm/shmem.c b/mm/shmem.c > index b16d3e7..8aa4892 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1341,6 +1341,35 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf) > return ret; > } > > +int shmem_locate(struct vm_area_struct *vma, pgoff_t pgoff, int *count) I don't find that a helpful name; but in 5/5 I question the info you're gathering here - maybe a good name will be more obvious once we've cut down what it's gathering. I just noticed that in 5/5 you're using a walk->pte_hole across empty extents: perhaps I'm prematurely optimizing, but that feels very inefficient, maybe here you should use a radix_tree lookup of the extent. If all we had to look up were the number of swap entries, in the vast majority of cases shmem.c could just see info->swapped is 0 and spend no time on radix_tree lookups at all. But what happens here depends on what really needs to be shown in 5/5. Hugh -- 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