Re: Accounting problem of MIGRATE_ISOLATED freed page
From: Aaditya Kumar
Date: Thu Jun 21 2012 - 07:02:47 EST
On Thu, Jun 21, 2012 at 10:25 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> On 06/21/2012 11:45 AM, KOSAKI Motohiro wrote:
>
>> On Wed, Jun 20, 2012 at 9:55 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
>>> On 06/21/2012 10:39 AM, KOSAKI Motohiro wrote:
>>>
>>>>>> number of isolate page block is almost always 0. then if we have such counter,
>>>>>> we almost always can avoid zone->lock. Just idea.
>>>>>
>>>>> Yeb. I thought about it but unfortunately we can't have a counter for MIGRATE_ISOLATE.
>>>>> Because we have to tweak in page free path for pages which are going to free later after we
>>>>> mark pageblock type to MIGRATE_ISOLATE.
>>>>
>>>> I mean,
>>>>
>>>> if (nr_isolate_pageblock != 0)
>>>> free_pages -= nr_isolated_free_pages(); // your counting logic
>>>>
>>>> return __zone_watermark_ok(z, alloc_order, mark,
>>>> classzone_idx, alloc_flags, free_pages);
>>>>
>>>>
>>>> I don't think this logic affect your race. zone_watermark_ok() is already
>>>> racy. then new little race is no big matter.
>>>
>>>
>>> It seems my explanation wasn't enough. :(
>>> I already understand your intention but we can't make nr_isolate_pageblock.
>>> Because we should count two type of free pages.
>>
>> I mean, move_freepages_block increment number of page *block*, not pages.
>> number of free *pages* are counted by zone_watermark_ok_safe().
>>
>>
>>> 1. Already freed page so they are already in buddy list.
>>> Of course, we can count it with return value of move_freepages_block(zone, page, MIGRATE_ISOLATE) easily.
>>>
>>> 2. Will be FREEed page by do_migrate_range.
>>> It's a _PROBLEM_. For it, we should tweak free path. No?
>>
>> No.
>>
>>
>>> If All of pages are PageLRU when hot-plug happens(ie, 2), nr_isolate_pagblock is zero and
>>> zone_watermk_ok_safe can't do his role.
>>
>> number of isolate pageblock don't depend on number of free pages. It's
>> a concept of
>> an attribute of PFN range.
>
>
> It seems you mean is_migrate_isolate as a just flag, NOT nr_isolate_pageblock.
> So do you mean this?
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 3bdcab3..7f4d19c 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -1,6 +1,7 @@
> #ifndef __LINUX_PAGEISOLATION_H
> #define __LINUX_PAGEISOLATION_H
>
> +extern bool is_migrate_isolate;
> /*
> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
> * If specified range includes migrate types other than MOVABLE or CMA,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d2a515d..b997cb3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1756,6 +1756,27 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long ma
> if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
> free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
>
> +#if defined CONFIG_CMA || CONFIG_MEMORY_HOTPLUG
> + if (unlikely(is_migrate_isolate)) {
> + unsigned long flags;
> + spin_lock_irqsave(&z->lock, flags);
> + for (order = MAX_ORDER - 1; order >= 0; order--) {
> + struct free_area *area = &z->free_area[order];
> + long count = 0;
> + struct list_head *curr;
> +
> + list_for_each(curr, &area->free_list[MIGRATE_ISOLATE])
> + count++;
> +
> + free_pages -= (count << order);
> + if (free_pages < 0) {
> + free_pages = 0;
> + break;
> + }
> + }
> + spin_unlock_irqrestore(&z->lock, flags);
> + }
> +#endif
> return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
> free_pages);
> }
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index c9f0477..212e526 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -19,6 +19,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> return pfn_to_page(pfn + i);
> }
>
> +bool is_migrate_isolate = false;
> +
> /*
> * start_isolate_page_range() -- make page-allocation-type of range of pages
> * to be MIGRATE_ISOLATE.
> @@ -43,6 +45,8 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> BUG_ON((start_pfn) & (pageblock_nr_pages - 1));
> BUG_ON((end_pfn) & (pageblock_nr_pages - 1));
>
> + is_migrate_isolate = true;
> +
> for (pfn = start_pfn;
> pfn < end_pfn;
> pfn += pageblock_nr_pages) {
> @@ -59,6 +63,7 @@ undo:
> pfn += pageblock_nr_pages)
> unset_migratetype_isolate(pfn_to_page(pfn), migratetype);
>
> + is_migrate_isolate = false;
> return -EBUSY;
> }
>
> @@ -80,6 +85,9 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> continue;
> unset_migratetype_isolate(page, migratetype);
> }
> +
> + is_migrate_isolate = false;
> +
> return 0;
> }
> /*
>
Hello Minchan,
Sorry for delayed response.
Instead of above how about something like this:
diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 3bdcab3..fe9215f 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -34,4 +34,6 @@ extern int set_migratetype_isolate(struct page *page);
extern void unset_migratetype_isolate(struct page *page, unsigned migratetype);
+extern atomic_t is_migrate_isolated;
+
#endif
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ab1e714..e076fa2 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1381,6 +1381,7 @@ static int get_any_page(struct page *p, unsigned
long pfn, int flags)
* Isolate the page, so that it doesn't get reallocated if it
* was free.
*/
+ atomic_inc(&is_migrate_isolated);
set_migratetype_isolate(p);
/*
* When the target page is a free hugepage, just remove it
@@ -1406,6 +1407,7 @@ static int get_any_page(struct page *p, unsigned
long pfn, int flags)
}
unset_migratetype_isolate(p, MIGRATE_MOVABLE);
unlock_memory_hotplug();
+ atomic_dec(&is_migrate_isolated);
return ret;
}
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0d7e3ec..cd7805c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -892,6 +892,7 @@ static int __ref offline_pages(unsigned long start_pfn,
nr_pages = end_pfn - start_pfn;
/* set above range as isolated */
+ atomic_inc(&is_migrate_isolated);
ret = start_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
if (ret)
goto out;
@@ -958,6 +959,7 @@ repeat:
offline_isolated_pages(start_pfn, end_pfn);
/* reset pagetype flags and makes migrate type to be MOVABLE */
undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
+ atomic_dec(&is_migrate_isolated);
/* removal success */
zone->present_pages -= offlined_pages;
zone->zone_pgdat->node_present_pages -= offlined_pages;
@@ -986,6 +988,7 @@ failed_removal:
undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
out:
+ atomic_dec(&is_migrate_isolated);
unlock_memory_hotplug();
return ret;
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4403009..f549361 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1632,6 +1632,28 @@ bool zone_watermark_ok_safe(struct zone *z, int
order, unsigned long mark,
if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
+#if defined CONFIG_CMA || CONFIG_MEMORY_HOTPLUG
+ if (unlikely(atomic_read(is_migrate_isolated)) {
+ unsigned long flags;
+ spin_lock_irqsave(&z->lock, flags);
+ for (order = MAX_ORDER - 1; order >= 0; order--) {
+ struct free_area *area = &z->free_area[order];
+ long count = 0;
+ struct list_head *curr;
+
+ list_for_each(curr, &area->free_list[MIGRATE_ISOLATE])
+ count++;
+
+ free_pages -= (count << order);
+ if (free_pages < 0) {
+ free_pages = 0;
+ break;
+ }
+ }
+ spin_unlock_irqrestore(&z->lock, flags);
+ }
+#endif
+
return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
free_pages);
}
@@ -5785,6 +5807,7 @@ int alloc_contig_range(unsigned long start,
unsigned long end,
* put back to page allocator so that buddy can use them.
*/
+ atomic_inc(&is_migrate_isolated);
ret = start_isolate_page_range(pfn_max_align_down(start),
pfn_max_align_up(end), migratetype);
if (ret)
@@ -5854,6 +5877,7 @@ int alloc_contig_range(unsigned long start,
unsigned long end,
done:
undo_isolate_page_range(pfn_max_align_down(start),
pfn_max_align_up(end), migratetype);
+ atomic_dec(&is_migrate_isolated);
return ret;
}
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c9f0477..e8eb241 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -19,6 +19,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
return pfn_to_page(pfn + i);
}
+atomic_t is_migrate_isolated;
+
/*
* start_isolate_page_range() -- make page-allocation-type of range of pages
* to be MIGRATE_ISOLATE.
> It is still racy as you already mentioned and I don't think it's trivial.
> Direct reclaim can't wake up kswapd forever by current fragile zone->all_unreclaimable.
> So it's a livelock.
> Then, do you want to fix this problem by your patch[1]?
>
> It could solve the livelock by OOM kill if we apply your patch[1] but still doesn't wake up
> kswapd although it's not critical. Okay. Then, please write down this problem in detail
> in your patch's changelog and resend, please.
>
> [1] http://lkml.org/lkml/2012/6/14/74
>
> --
> Kind regards,
> Minchan Kim
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