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Message-ID: <20171019122118.y6cndierwl2vnguj@dhcp22.suse.cz>
Date: Thu, 19 Oct 2017 14:21:18 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: linux-mm@...ck.org, Michael Ellerman <mpe@...erman.id.au>,
Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>,
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 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>
---
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;
}
--
2.14.2
--
Michal Hocko
SUSE Labs
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