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Date: Thu, 26 Oct 2017 15:04:55 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Michal Hocko <mhocko@...nel.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, Michael Ellerman <mpe@...erman.id.au>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Reza Arbab <arbab@...ux.vnet.ibm.com>,
Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
qiuxishi@...wei.com, Igor Mammedov <imammedo@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages
On 10/19/2017 02:21 PM, Michal Hocko wrote:
> On Thu 19-10-17 10:20:41, Michal Hocko wrote:
>> On Thu 19-10-17 16:33:56, Joonsoo Kim wrote:
>>> On Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote:
>>>> On Thu 19-10-17 11:51:11, Joonsoo Kim wrote:
>> [...]
>>>>> Hello,
>>>>>
>>>>> This patch will break the CMA user. As you mentioned, CMA allocation
>>>>> itself isn't migrateable. So, after a single page is allocated through
>>>>> CMA allocation, has_unmovable_pages() will return true for this
>>>>> pageblock. Then, futher CMA allocation request to this pageblock will
>>>>> fail because it requires isolating the pageblock.
>>>>
>>>> Hmm, does this mean that the CMA allocation path depends on
>>>> has_unmovable_pages to return false here even though the memory is not
>>>> movable? This sounds really strange to me and kind of abuse of this
>>>
>>> Your understanding is correct. Perhaps, abuse or wrong function name.
>>>
>>>> function. Which path is that? Can we do the migrate type test theres?
>>>
>>> alloc_contig_range() -> start_isolate_page_range() ->
>>> set_migratetype_isolate() -> has_unmovable_pages()
>>
>> I see. It seems that the CMA and memory hotplug have a very different
>> view on what should happen during isolation.
>>
>>> We can add one argument, 'XXX' to set_migratetype_isolate() and change
>>> it to check migrate type rather than has_unmovable_pages() if 'XXX' is
>>> specified.
>>
>> Can we use the migratetype argument and do the special thing for
>> MIGRATE_CMA? Like the following diff?
>
> And with the full changelog.
> ---
> From 8cbd811d741f5dd93d1b21bb3ef94482a4d0bd32 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Thu, 19 Oct 2017 14:14:02 +0200
> Subject: [PATCH] mm: distinguish CMA and MOVABLE isolation in
> has_unmovable_pages
>
> Joonsoo has noticed that "mm: drop migrate type checks from
> has_unmovable_pages" would break CMA allocator because it relies on
> has_unmovable_pages returning false even for CMA pageblocks which in
> fact don't have to be movable:
> alloc_contig_range
> start_isolate_page_range
> set_migratetype_isolate
> has_unmovable_pages
>
> This is a result of the code sharing between CMA and memory hotplug
> while each one has a different idea of what has_unmovable_pages should
> return. This is unfortunate but fixing it properly would require a lot
> of code duplication.
>
> Fix the issue by introducing the requested migrate type argument
> and special case MIGRATE_CMA case where CMA page blocks are handled
> properly. This will work for memory hotplug because it requires
> MIGRATE_MOVABLE.
>
> Reported-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> include/linux/page-isolation.h | 2 +-
> mm/page_alloc.c | 12 +++++++++++-
> mm/page_isolation.c | 10 +++++-----
> 3 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index d4cd2014fa6f..fa9db0c7b54e 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -30,7 +30,7 @@ static inline bool is_migrate_isolate(int migratetype)
> #endif
>
> bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> - bool skip_hwpoisoned_pages);
> + int migratetype, bool skip_hwpoisoned_pages);
> void set_pageblock_migratetype(struct page *page, int migratetype);
> int move_freepages_block(struct zone *zone, struct page *page,
> int migratetype, int *num_movable);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b4d85ae445c..259aeb22462f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7344,6 +7344,7 @@ void *__init alloc_large_system_hash(const char *tablename,
> * race condition. So you can't expect this function should be exact.
> */
> bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> + int migratetype,
> bool skip_hwpoisoned_pages)
> {
> unsigned long pfn, iter, found;
> @@ -7356,6 +7357,15 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> if (zone_idx(zone) == ZONE_MOVABLE)
> return false;
>
> + /*
> + * CMA allocations (alloc_contig_range) really need to mark isolate
> + * CMA pageblocks even when they are not movable in fact so consider
> + * them movable here.
> + */
> + if (is_migrate_cma(migratetype) &&
> + is_migrate_cma(get_pageblock_migratetype(page)))
> + return false;
> +
> pfn = page_to_pfn(page);
> for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
> unsigned long check = pfn + iter;
> @@ -7441,7 +7451,7 @@ bool is_pageblock_removable_nolock(struct page *page)
> if (!zone_spans_pfn(zone, pfn))
> return false;
>
> - return !has_unmovable_pages(zone, page, 0, true);
> + return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, true);
> }
>
> #if (defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) || defined(CONFIG_CMA)
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 757410d9f758..8616f5332c77 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -14,7 +14,7 @@
> #define CREATE_TRACE_POINTS
> #include <trace/events/page_isolation.h>
>
> -static int set_migratetype_isolate(struct page *page,
> +static int set_migratetype_isolate(struct page *page, int migratetype,
> bool skip_hwpoisoned_pages)
> {
> struct zone *zone;
> @@ -51,7 +51,7 @@ static int set_migratetype_isolate(struct page *page,
> * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
> * We just check MOVABLE pages.
> */
> - if (!has_unmovable_pages(zone, page, arg.pages_found,
> + if (!has_unmovable_pages(zone, page, arg.pages_found, migratetype,
> skip_hwpoisoned_pages))
> ret = 0;
>
> @@ -63,14 +63,14 @@ static int set_migratetype_isolate(struct page *page,
> out:
> if (!ret) {
> unsigned long nr_pages;
> - int migratetype = get_pageblock_migratetype(page);
> + int mt = get_pageblock_migratetype(page);
>
> set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> zone->nr_isolate_pageblock++;
> nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
> NULL);
>
> - __mod_zone_freepage_state(zone, -nr_pages, migratetype);
> + __mod_zone_freepage_state(zone, -nr_pages, mt);
> }
>
> spin_unlock_irqrestore(&zone->lock, flags);
> @@ -182,7 +182,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> pfn += pageblock_nr_pages) {
> page = __first_valid_page(pfn, pageblock_nr_pages);
> if (page &&
> - set_migratetype_isolate(page, skip_hwpoisoned_pages)) {
> + set_migratetype_isolate(page, migratetype, skip_hwpoisoned_pages)) {
> undo_pfn = pfn;
> goto undo;
> }
>
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