From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758100Ab2EWJVh (ORCPT ); Wed, 23 May 2012 05:21:37 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50998 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750981Ab2EWJVe (ORCPT ); Wed, 23 May 2012 05:21:34 -0400 Date: Wed, 23 May 2012 11:21:13 +0200 From: Jan Kara To: Akinobu Mita Cc: 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, Jan Kara , linux-ext4@vger.kernel.org, Andreas Dilger , "Theodore Ts'o" Subject: Re: [PATCH 01/10] string: introduce memweight Message-ID: <20120523092113.GG10452@quack.suse.cz> References: <1337520203-29147-1-git-send-email-akinobu.mita@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1337520203-29147-1-git-send-email-akinobu.mita@gmail.com> 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 Sun 20-05-12 22:23:14, Akinobu Mita wrote: > memweight() is the function that counts the total number of bits set > in memory area. The memory area doesn't need to be aligned to > long-word boundary unlike bitmap_weight(). Thanks for the patch. I have some comments below. > 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" > --- > include/linux/string.h | 3 +++ > lib/string.c | 37 +++++++++++++++++++++++++++++++++++++ > 2 files changed, 40 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..c8b92a0 100644 > --- a/lib/string.c > +++ b/lib/string.c > @@ -26,6 +26,7 @@ > #include > #include > #include > +#include > > #ifndef __HAVE_ARCH_STRNICMP > /** > @@ -824,3 +825,39 @@ 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; > + union { > + const void *ptr; > + const unsigned char *b; > + unsigned long address; > + } bitmap; Ugh, this is ugly and mostly unnecessary. Just use "const unsigned char *bitmap". > + > + for (bitmap.ptr = ptr; bytes > 0 && bitmap.address % sizeof(long); > + bytes--, bitmap.address++) > + w += hweight8(*bitmap.b); This can be: count = ((unsigned long)bitmap) % sizeof(long); while (count--) { w += hweight(*bitmap); bitmap++; bytes--; } > + > + for (longs = bytes / sizeof(long); longs > 0; ) { > + size_t bits = min_t(size_t, INT_MAX & ~(BITS_PER_LONG - 1), > + longs * BITS_PER_LONG); I find it highly unlikely that someone would have such a large bitmap (256 MB or more on 32-bit). Also the condition as you wrote it can just overflow so it won't have the desired effect. Just do BUG_ON(longs >= ULONG_MAX / BITS_PER_LONG); and remove the loop completely. If someone comes with such a huge bitmap, the code can be modified easily (after really closely inspecting whether such a huge bitmap is really well justified). > + > + w += bitmap_weight(bitmap.ptr, bits); > + bytes -= bits / BITS_PER_BYTE; > + bitmap.address += bits / BITS_PER_BYTE; > + longs -= bits / BITS_PER_LONG; > + } > + > + for (; bytes > 0; bytes--, bitmap.address++) > + w += hweight8(*bitmap.b); > + > + return w; > +} > +EXPORT_SYMBOL(memweight); Honza -- Jan Kara SUSE Labs, CR