From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f174.google.com (mail-pf0-f174.google.com [209.85.192.174]) by kanga.kvack.org (Postfix) with ESMTP id CE0996B0258 for ; Fri, 4 Dec 2015 21:36:38 -0500 (EST) Received: by pfnn128 with SMTP id n128so34829521pfn.0 for ; Fri, 04 Dec 2015 18:36:38 -0800 (PST) Received: from m50-132.163.com (m50-132.163.com. [123.125.50.132]) by mx.google.com with ESMTP id he9si23299527pac.102.2015.12.04.18.36.36 for ; Fri, 04 Dec 2015 18:36:37 -0800 (PST) Date: Sat, 5 Dec 2015 10:36:27 +0800 From: Geliang Tang Subject: Re: [PATCH v2] mm/slab.c: use list_{empty_careful,last_entry} in drain_freelist Message-ID: <20151205023627.GA9812@bogon> References: <3ea815dc52bf1a2bb5e324d7398315597900be84.1449151365.git.geliangtang@163.com> <20151204134302.GA6388@bogon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Geliang Tang On Fri, Dec 04, 2015 at 10:16:38AM -0600, Christoph Lameter wrote: > On Fri, 4 Dec 2015, Geliang Tang wrote: > > > On Thu, Dec 03, 2015 at 08:53:21AM -0600, Christoph Lameter wrote: > > > On Thu, 3 Dec 2015, Geliang Tang wrote: > > > > > > > while (nr_freed < tofree && !list_empty(&n->slabs_free)) { > > > > > > > > spin_lock_irq(&n->list_lock); > > > > - p = n->slabs_free.prev; > > > > - if (p == &n->slabs_free) { > > > > + if (list_empty_careful(&n->slabs_free)) { > > > > > > We have taken the lock. Why do we need to be "careful"? list_empty() > > > shoudl work right? > > > > Yes. list_empty() is OK. > > > > > > > > > spin_unlock_irq(&n->list_lock); > > > > goto out; > > > > } > > > > > > > > - page = list_entry(p, struct page, lru); > > > > + page = list_last_entry(&n->slabs_free, struct page, lru); > > > > > > last??? > > > > The original code delete the page from the tail of slabs_free list. > > Maybe make the code clearer by using another method to get the page > pointer? > > > > > > > Would the the other new function that returns NULL on the empty list or > > > the pointer not be useful here too and save some code? > > > > Sorry, I don't really understand what do you mean. Can you please specify > > it a little bit? > > I take that back. list_empty is the best choice here. If we use list_empty(), there will be two list_empty() in the code: while (nr_freed < tofree && !list_empty(&n->slabs_free)) { spin_lock_irq(&n->list_lock); if (list_empty(&n->slabs_free)) { spin_unlock_irq(&n->list_lock); goto out; } page = list_last_entry(&n->slabs_free, struct page, lru); list_del(&page->lru); spin_unlock_irq(&n->list_lock); } Or can we drop the first list_empty() like this? It will function the same as the above code. while (nr_freed < tofree) { spin_lock_irq(&n->list_lock); if (list_empty(&n->slabs_free)) { spin_unlock_irq(&n->list_lock); goto out; } page = list_last_entry(&n->slabs_free, struct page, lru); list_del(&page->lru); spin_unlock_irq(&n->list_lock); } Please let me know which one is better? Thanks. - Geliang -- 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