+ mm-thp-introduce-foll_split_pmd.patch added to -mm tree

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The patch titled
     Subject: mm, thp: introduce FOLL_SPLIT_PMD
has been added to the -mm tree.  Its filename is
     mm-thp-introduce-foll_split_pmd.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-introduce-foll_split_pmd.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-introduce-foll_split_pmd.patch

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------------------------------------------------------
From: Song Liu <songliubraving@xxxxxx>
Subject: mm, thp: introduce FOLL_SPLIT_PMD

Introduce a new foll_flag: FOLL_SPLIT_PMD.  As the name says
FOLL_SPLIT_PMD splits huge pmd for given mm_struct, the underlying 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/20190726054654.1623433-4-songliubraving@xxxxxx
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <matthew.wilcox@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/mm.h |    1 +
 mm/gup.c           |    8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

--- a/include/linux/mm.h~mm-thp-introduce-foll_split_pmd
+++ a/include/linux/mm.h
@@ -2633,6 +2633,7 @@ struct page *follow_page(struct vm_area_
 #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:
--- a/mm/gup.c~mm-thp-introduce-foll_split_pmd
+++ a/mm/gup.c
@@ -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);
 		}
 
 		return ret ? ERR_PTR(ret) :
_

Patches currently in -mm which might be from songliubraving@xxxxxx are

mm-move-memcmp_pages-and-pages_identical.patch
uprobe-use-original-page-when-all-uprobes-are-removed.patch
mm-thp-introduce-foll_split_pmd.patch
uprobe-use-foll_split_pmd-instead-of-foll_split.patch




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