From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx133.postini.com [74.125.245.133]) by kanga.kvack.org (Postfix) with SMTP id 9A4796B005D for ; Tue, 4 Sep 2012 07:10:39 -0400 (EDT) Message-ID: <5045E0ED.1000402@parallels.com> Date: Tue, 4 Sep 2012 15:07:25 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v2] mm, slob: Drop usage of page->private for storing page-sized allocations References: <1346753637-13389-1-git-send-email-elezegarcia@gmail.com> <5045D4B9.9000909@parallels.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ezequiel Garcia Cc: linux-mm@kvack.org, Pekka Enberg , Christoph Lameter On 09/04/2012 02:34 PM, Ezequiel Garcia wrote: > Hi Glauber, > > On Tue, Sep 4, 2012 at 7:15 AM, Glauber Costa wrote: >> On 09/04/2012 02:13 PM, Ezequiel Garcia wrote: >>> This field was being used to store size allocation so it could be >>> retrieved by ksize(). However, it is a bad practice to not mark a page >>> as a slab page and then use fields for special purposes. >>> There is no need to store the allocated size and >>> ksize() can simply return PAGE_SIZE << compound_order(page). >> >> What happens for allocations smaller than a page? >> It seems you are breaking ksize for those. >> > > Allocations smaller than a page save its own size on a header > located at each returned pointer. This is documented at the beginning of slob: > > "Above this is an implementation of kmalloc/kfree. Blocks returned > from kmalloc are prepended with a 4-byte header with the kmalloc size." > > For this objects (smaller than a page) ksize works fine: > > size_t ksize(const void *block) { > [...] > unsigned int *m = (unsigned int *)(block - align); > return SLOB_UNITS(*m) * SLOB_UNIT; > > (see how ksize substract 'align' from block to find the header?) > > Of course, it's possible I've overlooked something, but I think this > should work. > Ok. Slob also goes to the page allocator for higher order kmallocs, so it should work. -- 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