From: Minchan Kim <minchan@kernel.org> To: Vlastimil Babka <vbabka@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jlayton@poochiereds.net, bfields@fieldses.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>, koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Rik van Riel <riel@redhat.com>, rknize@motorola.com, Gioh Kim <gi-oh.kim@profitbricks.com>, Sangseok Lee <sangseok.lee@lge.com>, Chan Gyun Jeong <chan.jeong@lge.com>, Al Viro <viro@ZenIV.linux.org.uk>, YiPing Xu <xuyiping@hisilicon.com>, Jonathan Corbet <corbet@lwn.net> Subject: Re: [PATCH v3 03/16] mm: add non-lru movable page support document Date: Thu, 7 Apr 2016 11:27:14 +0900 [thread overview] Message-ID: <20160407022714.GC15178@bbox> (raw) In-Reply-To: <57026782.3020201@suse.cz> On Mon, Apr 04, 2016 at 03:09:22PM +0200, Vlastimil Babka wrote: > On 04/04/2016 04:25 AM, Minchan Kim wrote: > >> > >>Ah, I see, so it's designed with page lock to handle the concurrent isolations etc. > >> > >>In http://marc.info/?l=linux-mm&m=143816716511904&w=2 Mel has warned > >>about doing this in general under page_lock and suggested that each > >>user handles concurrent calls to isolate_page() internally. Might be > >>more generic that way, even if all current implementers will > >>actually use the page lock. > > > >We need PG_lock for two reasons. > > > >Firstly, it guarantees page's flags operation(i.e., PG_movable, PG_isolated) > >atomicity. Another thing is for stability for page->mapping->a_ops. > > > >For example, > > > >isolate_migratepages_block > > if (PageMovable(page)) > > isolate_movable_page > > get_page_unless_zero <--- 1 > > trylock_page > > page->mapping->a_ops->isolate_page <--- 2 > > > >Between 1 and 2, driver can nullify page->mapping so we need PG_lock > > Hmm I see, that really doesn't seem easily solvable without page_lock. > My idea is that compaction code would just check PageMovable() and > PageIsolated() to find a candidate. > page->mapping->a_ops->isolate_page would do the driver-specific > necessary locking, revalidate if the page state and succeed > isolation, or fail. It would need to handle the possibility that the So you mean that VM can try to isolate false-positive page of the driver? I don't think it's a good idea. For handling that, every driver should keep some logics to handle such false-positive which needs each own data structure or something to remember the page passed from VM is valid or not. It makes driver's logic more complicated and need more codes to handle it. It's not a good deal. > page already doesn't belong to the mapping, which is probably not a > problem. But what if the driver is a module that was already > unloaded, and even though we did NULL-check each part from page to > isolate_page, it points to a function that's already gone? That > would need some extra handling to prevent that, hm... Yes, driver should clean up pages is is using. For it, we need some lock. I think page_lock is good for it because we are migrating *page* and page_lock have been used it for a long time in migration path.
WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org> To: Vlastimil Babka <vbabka@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jlayton@poochiereds.net, bfields@fieldses.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>, koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Rik van Riel <riel@redhat.com>, rknize@motorola.com, Gioh Kim <gi-oh.kim@profitbricks.com>, Sangseok Lee <sangseok.lee@lge.com>, Chan Gyun Jeong <chan.jeong@lge.com>, Al Viro <viro@ZenIV.linux.org.uk>, YiPing Xu <xuyiping@hisilicon.com>, Jonathan Corbet <corbet@lwn.net> Subject: Re: [PATCH v3 03/16] mm: add non-lru movable page support document Date: Thu, 7 Apr 2016 11:27:14 +0900 [thread overview] Message-ID: <20160407022714.GC15178@bbox> (raw) In-Reply-To: <57026782.3020201@suse.cz> On Mon, Apr 04, 2016 at 03:09:22PM +0200, Vlastimil Babka wrote: > On 04/04/2016 04:25 AM, Minchan Kim wrote: > >> > >>Ah, I see, so it's designed with page lock to handle the concurrent isolations etc. > >> > >>In http://marc.info/?l=linux-mm&m=143816716511904&w=2 Mel has warned > >>about doing this in general under page_lock and suggested that each > >>user handles concurrent calls to isolate_page() internally. Might be > >>more generic that way, even if all current implementers will > >>actually use the page lock. > > > >We need PG_lock for two reasons. > > > >Firstly, it guarantees page's flags operation(i.e., PG_movable, PG_isolated) > >atomicity. Another thing is for stability for page->mapping->a_ops. > > > >For example, > > > >isolate_migratepages_block > > if (PageMovable(page)) > > isolate_movable_page > > get_page_unless_zero <--- 1 > > trylock_page > > page->mapping->a_ops->isolate_page <--- 2 > > > >Between 1 and 2, driver can nullify page->mapping so we need PG_lock > > Hmm I see, that really doesn't seem easily solvable without page_lock. > My idea is that compaction code would just check PageMovable() and > PageIsolated() to find a candidate. > page->mapping->a_ops->isolate_page would do the driver-specific > necessary locking, revalidate if the page state and succeed > isolation, or fail. It would need to handle the possibility that the So you mean that VM can try to isolate false-positive page of the driver? I don't think it's a good idea. For handling that, every driver should keep some logics to handle such false-positive which needs each own data structure or something to remember the page passed from VM is valid or not. It makes driver's logic more complicated and need more codes to handle it. It's not a good deal. > page already doesn't belong to the mapping, which is probably not a > problem. But what if the driver is a module that was already > unloaded, and even though we did NULL-check each part from page to > isolate_page, it points to a function that's already gone? That > would need some extra handling to prevent that, hm... Yes, driver should clean up pages is is using. For it, we need some lock. I think page_lock is good for it because we are migrating *page* and page_lock have been used it for a long time in migration path. -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-04-07 2:27 UTC|newest] Thread overview: 185+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-03-30 7:11 [PATCH v3 00/16] Support non-lru page migration Minchan Kim 2016-03-30 7:11 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 01/16] mm: use put_page to free page instead of putback_lru_page Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-01 12:58 ` Vlastimil Babka 2016-04-01 12:58 ` Vlastimil Babka 2016-04-01 12:58 ` Vlastimil Babka 2016-04-04 1:39 ` Minchan Kim 2016-04-04 1:39 ` Minchan Kim 2016-04-04 1:39 ` Minchan Kim 2016-04-04 4:45 ` Naoya Horiguchi 2016-04-04 4:45 ` Naoya Horiguchi 2016-04-04 14:46 ` Vlastimil Babka 2016-04-04 14:46 ` Vlastimil Babka 2016-04-04 14:46 ` Vlastimil Babka 2016-04-05 1:54 ` Naoya Horiguchi 2016-04-05 1:54 ` Naoya Horiguchi 2016-04-05 1:54 ` Naoya Horiguchi 2016-04-05 8:20 ` Vlastimil Babka 2016-04-05 8:20 ` Vlastimil Babka 2016-04-05 8:20 ` Vlastimil Babka 2016-04-06 0:54 ` Naoya Horiguchi 2016-04-06 0:54 ` Naoya Horiguchi 2016-04-06 0:54 ` Naoya Horiguchi 2016-04-06 7:57 ` Vlastimil Babka 2016-04-06 7:57 ` Vlastimil Babka 2016-04-06 7:57 ` Vlastimil Babka 2016-04-04 4:45 ` Naoya Horiguchi 2016-04-04 5:53 ` Balbir Singh 2016-04-04 5:53 ` Balbir Singh 2016-04-04 5:53 ` Balbir Singh 2016-04-04 6:01 ` Minchan Kim 2016-04-04 6:01 ` Minchan Kim 2016-04-04 6:01 ` Minchan Kim 2016-04-05 3:10 ` Balbir Singh 2016-04-05 3:10 ` Balbir Singh 2016-04-05 3:10 ` Balbir Singh 2016-03-30 7:12 ` [PATCH v3 02/16] mm/compaction: support non-lru movable page migration Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-01 21:29 ` Vlastimil Babka 2016-04-01 21:29 ` Vlastimil Babka 2016-04-04 5:12 ` Minchan Kim 2016-04-04 5:12 ` Minchan Kim 2016-04-04 13:24 ` Vlastimil Babka 2016-04-04 13:24 ` Vlastimil Babka 2016-04-04 13:24 ` Vlastimil Babka 2016-04-07 2:35 ` Minchan Kim 2016-04-07 2:35 ` Minchan Kim 2016-04-07 2:35 ` Minchan Kim 2016-04-04 13:24 ` Vlastimil Babka 2016-04-04 5:12 ` Minchan Kim 2016-04-01 21:29 ` Vlastimil Babka 2016-04-12 8:00 ` Chulmin Kim 2016-04-12 8:00 ` Chulmin Kim 2016-04-12 14:25 ` Minchan Kim 2016-04-12 14:25 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 03/16] mm: add non-lru movable page support document Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-01 14:38 ` Vlastimil Babka 2016-04-01 14:38 ` Vlastimil Babka 2016-04-01 14:38 ` Vlastimil Babka 2016-04-04 2:25 ` Minchan Kim 2016-04-04 2:25 ` Minchan Kim 2016-04-04 2:25 ` Minchan Kim 2016-04-04 13:09 ` Vlastimil Babka 2016-04-04 13:09 ` Vlastimil Babka 2016-04-04 13:09 ` Vlastimil Babka 2016-04-07 2:27 ` Minchan Kim 2016-04-07 2:27 ` Minchan Kim [this message] 2016-04-07 2:27 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 04/16] mm/balloon: use general movable page feature into balloon Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-05 12:03 ` Vlastimil Babka 2016-04-05 12:03 ` Vlastimil Babka 2016-04-05 12:03 ` Vlastimil Babka 2016-04-11 4:29 ` Minchan Kim 2016-04-11 4:29 ` Minchan Kim 2016-04-11 4:29 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 05/16] zsmalloc: keep max_object in size_class Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-17 15:08 ` Sergey Senozhatsky 2016-04-17 15:08 ` Sergey Senozhatsky 2016-04-17 15:08 ` Sergey Senozhatsky 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 06/16] zsmalloc: squeeze inuse into page->mapping Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-17 15:08 ` Sergey Senozhatsky 2016-04-17 15:08 ` Sergey Senozhatsky 2016-04-17 15:08 ` Sergey Senozhatsky 2016-04-19 7:40 ` Minchan Kim 2016-04-19 7:40 ` Minchan Kim 2016-04-19 7:40 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 07/16] zsmalloc: remove page_mapcount_reset Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-17 15:11 ` Sergey Senozhatsky 2016-04-17 15:11 ` Sergey Senozhatsky 2016-04-17 15:11 ` Sergey Senozhatsky 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 08/16] zsmalloc: squeeze freelist into page->mapping Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-17 15:56 ` Sergey Senozhatsky 2016-04-17 15:56 ` Sergey Senozhatsky 2016-04-17 15:56 ` Sergey Senozhatsky 2016-04-19 7:42 ` Minchan Kim 2016-04-19 7:42 ` Minchan Kim 2016-04-19 7:42 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 09/16] zsmalloc: move struct zs_meta from mapping to freelist Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-17 15:22 ` Sergey Senozhatsky 2016-04-17 15:22 ` Sergey Senozhatsky 2016-04-17 15:22 ` Sergey Senozhatsky 2016-03-30 7:12 ` [PATCH v3 10/16] zsmalloc: factor page chain functionality out Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-18 0:33 ` Sergey Senozhatsky 2016-04-18 0:33 ` Sergey Senozhatsky 2016-04-19 7:46 ` Minchan Kim 2016-04-19 7:46 ` Minchan Kim 2016-04-19 7:46 ` Minchan Kim 2016-04-18 0:33 ` Sergey Senozhatsky 2016-03-30 7:12 ` [PATCH v3 11/16] zsmalloc: separate free_zspage from putback_zspage Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-18 1:04 ` Sergey Senozhatsky 2016-04-18 1:04 ` Sergey Senozhatsky 2016-04-19 7:51 ` Minchan Kim 2016-04-19 7:51 ` Minchan Kim 2016-04-19 7:53 ` Sergey Senozhatsky 2016-04-19 7:53 ` Sergey Senozhatsky 2016-04-19 7:53 ` Sergey Senozhatsky 2016-04-19 7:51 ` Minchan Kim 2016-04-18 1:04 ` Sergey Senozhatsky 2016-03-30 7:12 ` [PATCH v3 12/16] zsmalloc: zs_compact refactoring Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-04 8:04 ` Chulmin Kim 2016-04-04 8:04 ` Chulmin Kim 2016-04-04 9:01 ` Minchan Kim 2016-04-04 9:01 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 13/16] zsmalloc: migrate head page of zspage Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-04-06 13:01 ` Chulmin Kim 2016-04-06 13:01 ` Chulmin Kim 2016-04-07 0:34 ` Chulmin Kim 2016-04-07 0:34 ` Chulmin Kim 2016-04-07 0:43 ` Minchan Kim 2016-04-07 0:43 ` Minchan Kim 2016-04-19 6:08 ` Chulmin Kim 2016-04-19 6:08 ` Chulmin Kim 2016-04-19 6:15 ` Minchan Kim 2016-04-19 6:15 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 14/16] zsmalloc: use single linked list for page chain Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 15/16] zsmalloc: migrate tail pages in zspage Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` [PATCH v3 16/16] zram: use __GFP_MOVABLE for memory allocation Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 7:12 ` Minchan Kim 2016-03-30 23:11 ` [PATCH v3 00/16] Support non-lru page migration Andrew Morton 2016-03-30 23:11 ` Andrew Morton 2016-03-30 23:11 ` Andrew Morton 2016-03-31 0:29 ` Sergey Senozhatsky 2016-03-31 0:29 ` Sergey Senozhatsky 2016-03-31 0:29 ` Sergey Senozhatsky 2016-03-31 0:57 ` Minchan Kim 2016-03-31 0:57 ` Minchan Kim 2016-03-31 0:57 ` Minchan Kim 2016-03-31 0:57 ` Minchan Kim 2016-03-31 0:57 ` Minchan Kim 2016-03-31 0:57 ` Minchan Kim 2016-04-04 13:17 ` John Einar Reitan 2016-04-04 13:17 ` John Einar Reitan 2016-04-11 4:35 ` Minchan Kim 2016-04-11 4:35 ` Minchan Kim
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