mm, thp: introduce FOLL_SPLIT_PMD (bfe7b00d) · Commits · 戴 / test

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>

include/linux/mm.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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:

mm/gup.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -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) :

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