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mm, thp: introduce FOLL_SPLIT_PMD

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Introduce a new foll_flag: FOLL_SPLIT_PMD.  As the name says
FOLL_SPLIT_PMD splits huge pmd for given mm_struct, the underlining huge
page stays as-is.

FOLL_SPLIT_PMD is useful for cases where we need to use regular pages, but
would switch back to huge page and huge pmd on.  One of such example is
uprobe.  The following patches use FOLL_SPLIT_PMD in uprobe.

Link: http://lkml.kernel.org/r/20190815164525.1848545-4-songliubraving@fb.com
Signed-off-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Song Liu 2019-09-23 15:38:25 -07:00 committed by Linus Torvalds
parent fb4fb04ff4
commit bfe7b00de6
2 changed files with 7 additions and 2 deletions
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1
include/linux/mm.h
View File

@ -2591,6 +2591,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
#define FOLL_COW 0x4000 /* internal GUP flag */
#define FOLL_ANON 0x8000 /* don't do file mappings */
#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
/*
* NOTE on FOLL_LONGTERM:

8
mm/gup.c
View File

@ -384,7 +384,7 @@ retry_locked:
spin_unlock(ptl);
return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
}
if (flags & FOLL_SPLIT) {
if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
int ret;
page = pmd_page(*pmd);
if (is_huge_zero_page(page)) {
@ -393,7 +393,7 @@ retry_locked:
split_huge_pmd(vma, pmd, address);
if (pmd_trans_unstable(pmd))
ret = -EBUSY;
} else {
} else if (flags & FOLL_SPLIT) {
if (unlikely(!try_get_page(page))) {
spin_unlock(ptl);
return ERR_PTR(-ENOMEM);
@ -405,6 +405,10 @@ retry_locked:
put_page(page);
if (pmd_none(*pmd))
return no_page_table(vma, flags);
} else { /* flags & FOLL_SPLIT_PMD */
spin_unlock(ptl);
split_huge_pmd(vma, pmd, address);
ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
}
return ret ? ERR_PTR(ret) :