From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752726AbeBFRr6 (ORCPT ); Tue, 6 Feb 2018 12:47:58 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:53514 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752658AbeBFRro (ORCPT ); Tue, 6 Feb 2018 12:47:44 -0500 Subject: Re: [RFC PATCH v1 12/13] mm: split up release_pages into non-sentinel and sentinel passes To: Laurent Dufour , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: aaron.lu@intel.com, ak@linux.intel.com, akpm@linux-foundation.org, Dave.Dice@oracle.com, dave@stgolabs.net, khandual@linux.vnet.ibm.com, mgorman@suse.de, mhocko@kernel.org, pasha.tatashin@oracle.com, steven.sistare@oracle.com, yossi.lev@oracle.com References: <20180131230413.27653-1-daniel.m.jordan@oracle.com> <20180131230413.27653-13-daniel.m.jordan@oracle.com> <3287f5ca-ab17-6437-c0fd-b867d90f8c1f@linux.vnet.ibm.com> <8a56da6b-8a47-3dc9-9b01-eb92be9fd828@linux.vnet.ibm.com> From: Daniel Jordan Organization: Oracle Corporation Message-ID: Date: Tue, 6 Feb 2018 12:47:54 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <8a56da6b-8a47-3dc9-9b01-eb92be9fd828@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8796 signatures=668662 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1802060225 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/02/2018 12:00 PM, Laurent Dufour wrote: > On 02/02/2018 15:40, Laurent Dufour wrote: >> >> >> On 01/02/2018 00:04, daniel.m.jordan@oracle.com wrote: >>> A common case in release_pages is for the 'pages' list to be in roughly >>> the same order as they are in their LRU. With LRU batch locking, when a >>> sentinel page is removed, an adjacent non-sentinel page must be promoted >>> to a sentinel page to follow the locking scheme. So we can get behavior >>> where nearly every page in the 'pages' array is treated as a sentinel >>> page, hurting the scalability of this approach. >>> >>> To address this, split up release_pages into non-sentinel and sentinel >>> passes so that the non-sentinel pages can be locked with an LRU batch >>> lock before the sentinel pages are removed. >>> >>> For the prototype, just use a bitmap and a temporary outer loop to >>> implement this. >>> >>> Performance numbers from a single microbenchmark at this point in the >>> series are included in the next patch. >>> >>> Signed-off-by: Daniel Jordan >>> --- >>> mm/swap.c | 20 +++++++++++++++++++- >>> 1 file changed, 19 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/swap.c b/mm/swap.c >>> index fae766e035a4..a302224293ad 100644 >>> --- a/mm/swap.c >>> +++ b/mm/swap.c >>> @@ -731,6 +731,7 @@ void lru_add_drain_all(void) >>> put_online_cpus(); >>> } >>> >>> +#define LRU_BITMAP_SIZE 512 >>> /** >>> * release_pages - batched put_page() >>> * @pages: array of pages to release >>> @@ -742,16 +743,32 @@ void lru_add_drain_all(void) >>> */ >>> void release_pages(struct page **pages, int nr) >>> { >>> - int i; >>> + int h, i; >>> LIST_HEAD(pages_to_free); >>> struct pglist_data *locked_pgdat = NULL; >>> spinlock_t *locked_lru_batch = NULL; >>> struct lruvec *lruvec; >>> unsigned long uninitialized_var(flags); >>> + DECLARE_BITMAP(lru_bitmap, LRU_BITMAP_SIZE); >>> + >>> + VM_BUG_ON(nr > LRU_BITMAP_SIZE); >> >> While running your series rebased on v4.15-mmotm-2018-01-31-16-51, I'm >> hitting this VM_BUG sometimes on a ppc64 system where page size is set to 64K. > > I can't see any link between nr and LRU_BITMAP_SIZE, caller may pass a > larger list of pages which is not relative to the LRU list. You're correct, I used the hard-coded size to quickly prototype, just to see how this approach performs. That's unfortunate that it bit you. > To move forward seeing the benefit of this series with the SPF one, I > declared the bit map based on nr. This is still not a valid option but this > at least allows to process all the passed pages. Yes, the bitmap's not for the final version.