From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760625Ab2FDNfQ (ORCPT ); Mon, 4 Jun 2012 09:35:16 -0400 Received: from cantor2.suse.de ([195.135.220.15]:46613 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754032Ab2FDNfO (ORCPT ); Mon, 4 Jun 2012 09:35:14 -0400 Date: Mon, 4 Jun 2012 15:35:09 +0200 From: Jan Kara To: Akinobu Mita Cc: Jan Kara , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Anders Larsen , Alasdair Kergon , dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, Laurent Pinchart , linux-media@vger.kernel.org, Mark Fasheh , Joel Becker , ocfs2-devel@oss.oracle.com, linux-ext4@vger.kernel.org, Andreas Dilger , "Theodore Ts'o" , Matthew Wilcox Subject: Re: [PATCH v2 01/10] string: introduce memweight Message-ID: <20120604133509.GA11010@quack.suse.cz> References: <1338644416-11417-1-git-send-email-akinobu.mita@gmail.com> <20120604101237.GD7670@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 04-06-12 20:46:14, Akinobu Mita wrote: > 2012/6/4 Jan Kara : > > On Sat 02-06-12 22:40:07, Akinobu Mita wrote: > >> memweight() is the function that counts the total number of bits set > >> in memory area.  Unlike bitmap_weight(), memweight() takes pointer > >> and size in bytes to specify a memory area which does not need to be > >> aligned to long-word boundary. > >> > >> Signed-off-by: Akinobu Mita > >> Cc: Anders Larsen > >> Cc: Alasdair Kergon > >> Cc: dm-devel@redhat.com > >> Cc: linux-fsdevel@vger.kernel.org > >> Cc: Laurent Pinchart > >> Cc: linux-media@vger.kernel.org > >> Cc: Mark Fasheh > >> Cc: Joel Becker > >> Cc: ocfs2-devel@oss.oracle.com > >> Cc: Jan Kara > >> Cc: linux-ext4@vger.kernel.org > >> Cc: Andrew Morton > >> Cc: Andreas Dilger > >> Cc: "Theodore Ts'o" > >> Cc: Matthew Wilcox > >> --- > >> > >> v2: simplify memweight(), adviced by Jan Kara > >> > >>  include/linux/string.h |    3 +++ > >>  lib/string.c           |   32 ++++++++++++++++++++++++++++++++ > >>  2 files changed, 35 insertions(+), 0 deletions(-) > >> > >> diff --git a/include/linux/string.h b/include/linux/string.h > >> index e033564..ffe0442 100644 > >> --- a/include/linux/string.h > >> +++ b/include/linux/string.h > >> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix) > >>       return strncmp(str, prefix, strlen(prefix)) == 0; > >>  } > >>  #endif > >> + > >> +extern size_t memweight(const void *ptr, size_t bytes); > >> + > >>  #endif /* _LINUX_STRING_H_ */ > >> diff --git a/lib/string.c b/lib/string.c > >> index e5878de..bf4d5a8 100644 > >> --- a/lib/string.c > >> +++ b/lib/string.c > >> @@ -26,6 +26,7 @@ > >>  #include > >>  #include > >>  #include > >> +#include > >> > >>  #ifndef __HAVE_ARCH_STRNICMP > >>  /** > >> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes) > >>       return check_bytes8(start, value, bytes % 8); > >>  } > >>  EXPORT_SYMBOL(memchr_inv); > >> + > >> +/** > >> + * memweight - count the total number of bits set in memory area > >> + * @ptr: pointer to the start of the area > >> + * @bytes: the size of the area > >> + */ > >> +size_t memweight(const void *ptr, size_t bytes) > >> +{ > >> +     size_t w = 0; > >> +     size_t longs; > >> +     const unsigned char *bitmap = ptr; > >> + > >> +     for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long); > >> +                     bytes--, bitmap++) > >> +             w += hweight8(*bitmap); > >> + > >> +     longs = bytes / sizeof(long); > >> +     if (longs) { > >> +             BUG_ON(longs >= INT_MAX / BITS_PER_LONG); > >> +             w += bitmap_weight((unsigned long *)bitmap, > >> +                             longs * BITS_PER_LONG); > >> +             bytes -= longs * sizeof(long); > >> +             bitmap += longs * sizeof(long); > >> +     } > >> + > >> +     for (; bytes > 0; bytes--, bitmap++) > >> +             w += hweight8(*bitmap); > >  Looking at bitmap_weight() it seems this last loop is not needed. Just > > pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function > > doesn't seem necessary at all at least for ext2 & ext3 (sorry for not > > noticing this earlier...). > > This last loop is necessary for big-endian architecture. > if bytes % sizeof(long) != 0, bitmap_weight() counts one-bits in wrong > byte-field > of the last long word. Ah, right. OK. Add this to the comment before the loop please. You save yourself some explanations :) Honza -- Jan Kara SUSE Labs, CR