linux-kernel - Re: [PATCH 1/2] hugetlbfs: extend hugetlb_vma

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Date:   Fri, 22 Sep 2023 10:37:55 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        muchun.song@...ux.dev, leit@...a.com
Subject: Re: [PATCH 1/2] hugetlbfs: extend hugetlb_vma_lock to private VMAs

On Thu, 2023-09-21 at 15:42 -0700, Mike Kravetz wrote:
> On 09/19/23 22:16, riel@...riel.com wrote:
> > From: Rik van Riel <riel@...riel.com>
> > 
> > Extend the locking scheme used to protect shared hugetlb mappings
> > from truncate vs page fault races, in order to protect private
> > hugetlb mappings (with resv_map) against MADV_DONTNEED.
> > 
> > Add a read-write semaphore to the resv_map data structure, and
> > use that from the hugetlb_vma_(un)lock_* functions, in preparation
> > for closing the race between MADV_DONTNEED and page faults.
> > 
> > Signed-off-by: Rik van Riel <riel@...riel.com>
> > ---
> >  include/linux/hugetlb.h |  6 ++++++
> >  mm/hugetlb.c            | 36 ++++++++++++++++++++++++++++++++----
> >  2 files changed, 38 insertions(+), 4 deletions(-)
> 
> This looks straight forward.
> 
> However, I ran just this patch through libhugetlbfs test suite and it
> hung on
> misaligned_offset (2M: 32).
> https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/misaligned_offset.c


Speaking of "looks straightforward", how do I compile the
libhugetlbfs code?

The __morecore variable, which is pointed at either the
THP or hugetlbfs morecore function, does not seem to be
defined anywhere in the sources.

Do I need to run some magic script (didn't find it) to
get a special header file set up before I can build
libhugetlbfs?



$ make
	 CC32 obj32/morecore.o
morecore.c: In function ‘__lh_hugetlbfs_setup_morecore’:
morecore.c:368:17: error: ‘__morecore’ undeclared (first use in this
function); did you mean ‘thp_morecore’?
  368 |                 __morecore = &thp_morecore;
      |                 ^~~~~~~~~~
      |                 thp_morecore
morecore.c:368:17: note: each undeclared identifier is reported only
once for each function it appears in
make: *** [Makefile:292: obj32/morecore.o] Error 1
$ grep __morecore *.[ch]
morecore.c:		__morecore = &thp_morecore;
morecore.c:		__morecore = &hugetlbfs_morecore;



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