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Mike Kravetz 68d32527d3 hugetlbfs: zero partial pages during fallocate hole punch hugetlbfs fallocate support was originally added with commit `70c3547e36` ("hugetlbfs: add hugetlbfs_fallocate()"). Initial support only operated on whole hugetlb pages. This makes sense for populating files as other interfaces such as mmap and truncate require hugetlb page size alignment. Only operating on whole hugetlb pages for the hole punch case was a simplification and there was no compelling use case to zero partial pages. In a recent discussion[1] it was assumed that hugetlbfs hole punch would zero partial hugetlb pages as that is in line with the man page description saying 'partial filesystem blocks are zeroed'. However, the hugetlbfs hole punch code actually does this: hole_start = round_up(offset, hpage_size); hole_end = round_down(offset + len, hpage_size); Modify code to zero partial hugetlb pages in hole punch range. It is possible that application code could note a change in behavior. However, that would imply the code is passing in an unaligned range and expecting only whole pages be removed. This is unlikely as the fallocate documentation states the opposite. The current hugetlbfs fallocate hole punch behavior is tested with the libhugetlbfs test fallocate_align[2]. This test will be updated to validate partial page zeroing. [1] https://lore.kernel.org/linux-mm/20571829-9d3d-0b48-817c-b6b15565f651@redhat.com/ [2] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/fallocate_align.c Link: https://lkml.kernel.org/r/YqeiMlZDKI1Kabfe@monkey Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Cc: David Hildenbrand <david@redhat.com> Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>	2022-06-16 19:11:32 -07:00
..
Makefile	treewide: Add SPDX license identifier - Makefile/Kconfig	2019-05-21 10:50:46 +02:00
inode.c	hugetlbfs: zero partial pages during fallocate hole punch	2022-06-16 19:11:32 -07:00

Mike Kravetz 68d32527d3 hugetlbfs: zero partial pages during fallocate hole punch

hugetlbfs fallocate support was originally added with commit 70c3547e36
("hugetlbfs: add hugetlbfs_fallocate()").  Initial support only operated
on whole hugetlb pages.  This makes sense for populating files as other
interfaces such as mmap and truncate require hugetlb page size alignment. 
Only operating on whole hugetlb pages for the hole punch case was a
simplification and there was no compelling use case to zero partial pages.

In a recent discussion[1] it was assumed that hugetlbfs hole punch would
zero partial hugetlb pages as that is in line with the man page
description saying 'partial filesystem blocks are zeroed'.  However, the
hugetlbfs hole punch code actually does this:

        hole_start = round_up(offset, hpage_size);
        hole_end = round_down(offset + len, hpage_size);

Modify code to zero partial hugetlb pages in hole punch range.  It is
possible that application code could note a change in behavior.  However,
that would imply the code is passing in an unaligned range and expecting
only whole pages be removed.  This is unlikely as the fallocate
documentation states the opposite.

The current hugetlbfs fallocate hole punch behavior is tested with the
libhugetlbfs test fallocate_align[2].  This test will be updated to
validate partial page zeroing.

[1] https://lore.kernel.org/linux-mm/20571829-9d3d-0b48-817c-b6b15565f651@redhat.com/
[2] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/fallocate_align.c

Link: https://lkml.kernel.org/r/YqeiMlZDKI1Kabfe@monkey
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2022-06-16 19:11:32 -07:00

Makefile treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00

inode.c hugetlbfs: zero partial pages during fallocate hole punch 2022-06-16 19:11:32 -07:00