Re: [PATCH -mm][BUGFIX] migration_entry_wait fix. v2
- From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
- Date: Wed, 18 Jun 2008 16:26:09 +0900
In speculative page cache look up protocol, page_count(page) is set to 0
while radix-tree modification is going on, truncation, migration, etc...
While page migration, a page fault to page under migration does
- look up page table
- find it is migration_entry_pte
- decode pfn from migration_entry_pte and get page of pfn_page(pfn)
- wait until page is unlocked
It does get_page() -> wait_on_page_locked() -> put_page() now.
In page migration's radix-tree replacement, page_freeze_refs() ->
page_unfreeze_refs() is called. And page_count(page) turns to be zero
and must be kept to be zero while radix-tree replacement.
If get_page() is called against a page under radix-tree replacement,
the kernel panics(). To avoid this, we shouldn't increment page_count()
if it is zero. This patch uses get_page_unless_zero().
Even if get_page_unless_zero() fails, the caller just retries.
But will be a bit busier.
Great!
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
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- References:
- Re: [PATCH] migration_entry_wait fix.
- From: KAMEZAWA Hiroyuki
- [PATCH -mm][BUGFIX] migration_entry_wait fix. v2
- From: KAMEZAWA Hiroyuki
- Re: [PATCH] migration_entry_wait fix.
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