Re: WARNING: at mm/page-writeback.c:1990 __set_page_dirty_nobuffers+0x13a/0x170()

[Minchan Kim]

On 06/04/2012 08:13 AM, Linus Torvalds wrote:

> On Sun, Jun 3, 2012 at 3:17 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
>>
>> But another strike against that commit: I tried fixing it up to use
>> start_page instead of page at the end, with the worrying but safer
>> locking I suggested at first, with a count of how many times it went
>> there, and how many times it succeeded.
> 
> You can't use start_page anyway, it might not be a valid page. There's
> a reson it does that "pfn_valid_within()", methinks.


Right. I missed that. I think we can use the page passed to rescue_unmovable_pageblock.
We make sure it's valid in isolate_freepages. So how about this?

barrios@bbox:~/linux-2.6$ git diff
diff --git a/mm/compaction.c b/mm/compaction.c
index 4ac338a..7459ab5 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -368,11 +368,11 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 static bool rescue_unmovable_pageblock(struct page *page)
 {
        unsigned long pfn, start_pfn, end_pfn;
-       struct page *start_page, *end_page;
+       struct page *start_page, *end_page, *cursor_page;
 
        pfn = page_to_pfn(page);
        start_pfn = pfn & ~(pageblock_nr_pages - 1);
-       end_pfn = start_pfn + pageblock_nr_pages;
+       end_pfn = start_pfn + pageblock_nr_pages - 1;
 
        start_page = pfn_to_page(start_pfn);
        end_page = pfn_to_page(end_pfn);
@@ -381,19 +381,19 @@ static bool rescue_unmovable_pageblock(struct page *page)
        if (page_zone(start_page) != page_zone(end_page))
                return false;
 
-       for (page = start_page, pfn = start_pfn; page < end_page; pfn++,
-                                                                 page++) {
+       for (cursor_page = start_page, pfn = start_pfn; cursor_page <= end_page; pfn++,
+                                                                 cursor_page++) {
                if (!pfn_valid_within(pfn))
                        continue;
 
-               if (PageBuddy(page)) {
-                       int order = page_order(page);
+               if (PageBuddy(cursor_page)) {
+                       int order = page_order(cursor_page);
 
                        pfn += (1 << order) - 1;
-                       page += (1 << order) - 1;
+                       cursor_page += (1 << order) - 1;
 
                        continue;
-               } else if (page_count(page) == 0 || PageLRU(page))
+               } else if (page_count(cursor_page) == 0 || PageLRU(cursor_page))
                        continue;
 
                return false;


> 
> Anyway, my current plan is to apply your "mm: fix warning in
> __set_page_dirty_nobuffers" patch - even if it's just a harmless
> WARN_ON_ONCE(), and revert 5ceb9ce6fe94. Sounds like Dave hit normally
> hit his problem much before two hours, and it must be even longer now.

> 

> Ack on that plan?


No objection.
The patch wasn't a bug fix and even test workload was very theoretical.

> 
>         Linus
> 
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-- 
Kind regards,
Minchan Kim
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