Re: hugetlbfs not working

Marcelo Tosatti
2008-03-27T21:55:10Z

On Thu, Mar 27, 2008 at 06:09:56PM +0200, Avi Kivity wrote:
> Anthony Liguori wrote:
> >
> > If you don't bail when ftruncate fails, does it work as expected for
> > you? Perhaps older versions of hugetlbfs didn't support truncate.
>
> If you don't truncate, how can you change the file size? hugetlbfs
> doesn't support write().
>
> I vaugely recall using ftruncate() on 2.4.

commit 7aa91e104028b87ff13f5eeb7a0d7ffe7b5a2348
Author: Ken Chen <kenchen@google.com>
Date: Tue Oct 16 01:26:21 2007 -0700

hugetlb: allow extending ftruncate on hugetlbfs

For historical reason, expanding ftruncate that increases file size on
hugetlbfs is not allowed due to pages were pre-faulted and lack of fault
handler. Now that we have demand faulting on hugetlb since 2.6.15, there
is no reason to hold back that limitation.

This will make hugetlbfs behave more like a normal fs. I'm writing a user
level code that uses hugetlbfs but will fall back to tmpfs if there are no
hugetlb page available in the system. Having hugetlbfs specific ftruncate
behavior is a bit quirky and I would like to remove that artificial
limitation.

Signed-off-by: <kenchen@google.com>
Acked-by: Wiliam Irwin <wli@holomorphy.com>
Cc: Adam Litke <agl@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mmap() should fail if anything goes wrong with ftruncate and the file
length is not extented on tmpfs.

--- vl.c.orig 2008-03-27 18:51:31.000000000 -0300
+++ vl.c 2008-03-27 18:52:40.000000000 -0300
@@ -8749,11 +8749,7 @@

memory = (memory+hpagesize-1) & ~(hpagesize-1);

- if (ftruncate(fd, memory) == -1) {
- perror("ftruncate");
- close(fd);
- return NULL;
- }
+ ftruncate(fd, memory);

area = mmap(0, memory, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
if (area == MAP_FAILED) {