Re: [PATCH 3/3] mm, thp: make swapin readahead under down_read of mmap_sem
From: Rik van Riel <hidden>
Date: 2016-05-23 19:26:55
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On Mon, 2016-05-23 at 22:01 +0300, Kirill A. Shutemov wrote:
On Mon, May 23, 2016 at 02:49:09PM -0400, Rik van Riel wrote:quoted
On Mon, 2016-05-23 at 20:42 +0200, Michal Hocko wrote:quoted
On Mon 23-05-16 20:14:11, Ebru Akagunduz wrote:quoted
Currently khugepaged makes swapin readahead under down_write. This patch supplies to make swapin readahead under down_read instead of down_write.You are still keeping down_write. Can we do without it altogether? Blocking mmap_sem of a remote proces for write is certainly not nice.Maybe Andrea can explain why khugepaged requires a down_write of mmap_sem? If it were possible to have just down_read that would make the code a lot simpler.You need a down_write() to retract page table. We need to make sure that nobody sees the page table before we can replace it with huge pmd.
Good point. I guess the alternative is to have the page_table_lock taken by a helper function (everywhere) that can return failure if the page table was changed while the caller was waiting for the lock. Doable, but a fair amount of code churn. -- All Rights Reversed.
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