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Date: Thu, 10 Mar 2022 20:16:48 +0000
From: Matthew Wilcox <willy@infradead.org>
To: David Rientjes <rientjes@google.com>
Cc: Yang Shi <shy828301@gmail.com>, Zach O'Keefe <zokeefe@google.com>,
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Subject: Re: [RFC PATCH 12/14] mm/madvise: introduce batched
 madvise(MADV_COLLPASE) collapse
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On Thu, Mar 10, 2022 at 11:26:15AM -0800, David Rientjes wrote:
> One concern might be the queueing of read locks needed for page faults 
> behind a collapser of a long range of memory that is otherwise looping 
> and repeatedly taking the write lock.

I would have thought that _not_ batching would improve this situation.
Unless our implementation of rwsems has changed since the last time I
looked, dropping-and-reacquiring a rwsem while there are pending readers
means you go to the end of the line and they all get to handle their
page faults.