linux-kernel - RE: [PATCH 23/26] ib: Convert qib_get_user_pages() to get_user_pages

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Date:	Fri, 4 Oct 2013 13:52:49 +0000
From:	"Marciniszyn, Mike" <mike.marciniszyn@...el.com>
To:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	infinipath <infinipath@...el.com>,
	Roland Dreier <roland@...nel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: [PATCH 23/26] ib: Convert qib_get_user_pages() to
 get_user_pages_unlocked()

> Convert qib_get_user_pages() to use get_user_pages_unlocked().  This
> shortens the section where we hold mmap_sem for writing and also removes
> the knowledge about get_user_pages() locking from ipath driver. We also fix
> a bug in testing pinned number of pages when changing the code.
> 

This patch and the sibling ipath patch will nominally take the mmap_sem twice where the old routine only took it once.   This is a performance issue.

Is the intent here to deprecate get_user_pages()?

I agree, the old code's lock limit test is broke and needs to be fixed.   I like the elimination of the silly wrapper routine!

Could the lock limit test be pushed into another version of the wrapper so that there is only one set of mmap_sem transactions?

Mike
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