[PATCH v4 06/10] mm/hugetlb: vma_has_reserves() needs to handle fallocate hole punch
From: Mike Kravetz <hidden>
Date: 2015-07-21 18:11:35
Also in:
linux-mm, lkml
Subsystem:
hugetlb subsystem, memory management, the rest · Maintainers:
Muchun Song, Oscar Salvador, Andrew Morton, Linus Torvalds
In vma_has_reserves(), the current assumption is that reserves are always present for shared mappings. However, this will not be the case with fallocate hole punch. When punching a hole, the present page will be deleted as well as the region/reserve map entry (and hence any reservation). vma_has_reserves is passed "chg" which indicates whether or not a region/reserve map is present. Use this to determine if reserves are actually present or were removed via hole punch. Signed-off-by: Mike Kravetz <redacted> --- mm/hugetlb.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index db9caea..f9d3faf 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c@@ -803,8 +803,19 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg) } /* Shared mappings always use reserves */ - if (vma->vm_flags & VM_MAYSHARE) - return true; + if (vma->vm_flags & VM_MAYSHARE) { + /* + * We know VM_NORESERVE is not set. Therefore, there SHOULD + * be a region map for all pages. The only situation where + * there is no region map is if a hole was punched via + * fallocate. In this case, there really are no reverves to + * use. This situation is indicated if chg != 0. + */ + if (chg) + return false; + else + return true; + } /* * Only the process that called mmap() has reserves for
--
2.1.0
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