From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx128.postini.com [74.125.245.128]) by kanga.kvack.org (Postfix) with SMTP id A570F6B005D for ; Tue, 4 Sep 2012 06:34:39 -0400 (EDT) Received: by iec9 with SMTP id 9so5701835iec.14 for ; Tue, 04 Sep 2012 03:34:39 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <5045D4B9.9000909@parallels.com> References: <1346753637-13389-1-git-send-email-elezegarcia@gmail.com> <5045D4B9.9000909@parallels.com> Date: Tue, 4 Sep 2012 07:34:38 -0300 Message-ID: Subject: Re: [PATCH v2] mm, slob: Drop usage of page->private for storing page-sized allocations From: Ezequiel Garcia Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: linux-mm@kvack.org, Pekka Enberg , Christoph Lameter 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. Thanks! Ezequiel. -- 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