From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oren Laadan Subject: Re: [RFC v11][PATCH 05/13] Dump memory address space Date: Thu, 18 Dec 2008 15:00:27 -0500 Message-ID: <494AABDB.80408@cs.columbia.edu> References: <1228498282-11804-1-git-send-email-orenl@cs.columbia.edu> <1228498282-11804-6-git-send-email-orenl@cs.columbia.edu> <4949B4ED.9060805@google.com> <494A2F94.2090800@cs.columbia.edu> <1229615676.17206.518.camel@nimitz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1229615676.17206.518.camel@nimitz> Sender: owner-linux-mm@kvack.org To: Dave Hansen Cc: Mike Waychison , jeremy@goop.org, arnd@arndb.de, linux-api@vger.kernel.org, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linux Torvalds , Alexander Viro , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar List-Id: linux-api@vger.kernel.org Dave Hansen wrote: > On Thu, 2008-12-18 at 06:10 -0500, Oren Laadan wrote: >>>> + for (i = pgarr->nr_used; i--; /**/) >>>> + page_cache_release(pgarr->pages[i]); >>> This is sorta hard to read (and non-intuitive). Is it easier to do: >>> >>> for (i = 0; i < pgarr->nr_used; i++) >>> page_cache_release(pgarr->pages[i]); >>> >>> It shouldn't matter what order you release the pages in.. >> Was meant to avoid a dereference to 'pgarr->nr_used' in the comparison. >> (though I doubt if the performance impact is at all visible) > > That's a bit to aggressive an optimization. You two piqued my > curiosity, so I tried a little experiment with this .c file: > > extern void bar(int i); > > struct s { > int *array; > int size; > }; > > extern struct s *s; > void foo(void) > { > int i; > #ifdef OREN > for (i = s->size; i--; ) > #else > for (i = 0; i < s->size; i++) > #endif > bar(s->array[i]); > } > > for O in "" -O -O1 -O2 -O3 -Os; do > gcc -DOREN $O -c f1.c -o oren.o; > gcc $O -c f1.c -o mike.o; > echo -n Oren:; objdump -d oren.o | grep ret; > echo -n Mike:; objdump -d mike.o | grep ret; > done For what it's worth, the idea was to improve time... (not code length). I changed the code anyway (in response to another comment). Oren. -- 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