From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id ECACA6B0069 for ; Thu, 20 Oct 2016 18:33:37 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id 128so36915085pfz.1 for ; Thu, 20 Oct 2016 15:33:37 -0700 (PDT) Received: from ipmail05.adl6.internode.on.net (ipmail05.adl6.internode.on.net. [150.101.137.143]) by mx.google.com with ESMTP id rf4si39100191pab.9.2016.10.20.15.33.36 for ; Thu, 20 Oct 2016 15:33:37 -0700 (PDT) Date: Fri, 21 Oct 2016 09:33:08 +1100 From: Dave Chinner Subject: Re: [PATCH 3/5] lib: radix-tree: native accounting and tracking of special entries Message-ID: <20161020223308.GN23194@dastard> References: <20161019172428.7649-1-hannes@cmpxchg.org> <20161019172428.7649-4-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161019172428.7649-4-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Linus Torvalds , Jan Kara , Dave Jones , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Wed, Oct 19, 2016 at 01:24:26PM -0400, Johannes Weiner wrote: > Add an internal tag to identify special entries that are accounted in > node->special in addition to node->count. > > With this in place, the next patch can restore refault detection in > single-page files. It will also move the shadow count from the upper > bits of count to the new special counter, and then shrink count to a > char as well; the growth of struct radix_tree_node is temporary. > > Signed-off-by: Johannes Weiner > --- > include/linux/radix-tree.h | 10 ++++++---- > lib/radix-tree.c | 14 ++++++++++---- > 2 files changed, 16 insertions(+), 8 deletions(-) > > diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h > index 756b2909467e..2e1c9added23 100644 > --- a/include/linux/radix-tree.h > +++ b/include/linux/radix-tree.h > @@ -68,7 +68,8 @@ enum radix_tree_tags { > /* Freely allocatable radix tree user tags */ > RADIX_TREE_NR_USER_TAGS = 3, > /* Radix tree internal tags */ > - RADIX_TREE_NR_TAGS = RADIX_TREE_NR_USER_TAGS, > + RADIX_TREE_TAG_SPECIAL = RADIX_TREE_NR_USER_TAGS, > + RADIX_TREE_NR_TAGS, > }; > > #ifndef RADIX_TREE_MAP_SHIFT > @@ -90,9 +91,10 @@ enum radix_tree_tags { > #define RADIX_TREE_COUNT_MASK ((1UL << RADIX_TREE_COUNT_SHIFT) - 1) > > struct radix_tree_node { > - unsigned char shift; /* Bits remaining in each slot */ > - unsigned char offset; /* Slot offset in parent */ > - unsigned int count; > + unsigned char shift; /* Bits remaining in each slot */ > + unsigned char offset; /* Slot offset in parent */ > + unsigned int count; /* Total entry count */ > + unsigned char special; /* Special entry count */ How about putting the new char field into the implicit hole between offset and count? pahole is your friend here: struct radix_tree_node { unsigned char shift; /* 0 1 */ unsigned char offset; /* 1 1 */ /* XXX 2 bytes hole, try to pack */ unsigned int count; /* 4 4 */ ..... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- 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