Re: [PATCH 5/5] hugetlbfs: Limit wait time when trying to share huge PMD
From: Matthew Wilcox
Date: Wed Sep 11 2019 - 23:42:07 EST
On Wed, Sep 11, 2019 at 08:26:52PM -0700, Mike Kravetz wrote:
> All this got me wondering if we really need to take i_mmap_rwsem in write
> mode here. We are not changing the tree, only traversing it looking for
> a suitable vma.
> Unless I am missing something, the hugetlb code only ever takes the semaphore
> in write mode; never read. Could this have been the result of changing the
> tree semaphore to read/write? Instead of analyzing all the code, the easiest
> and safest thing would have been to take all accesses in write mode.
I was wondering the same thing. It was changed here:
Author: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Date: Fri Dec 12 16:54:21 2014 -0800
mm: use new helper functions around the i_mmap_mutex
Convert all open coded mutex_lock/unlock calls to the
and a subsequent patch said:
This conversion is straightforward. For now, all users take the write
There were subsequent patches which changed a few places
but I don't know why this one wasn't changed.
(I was also wondering about caching a potentially sharable page table
in the address_space to avoid having to walk the VMA tree at all if that
one happened to be sharable).