[054/178] mm: gup: remove FOLL_SPLIT

Commit Message

Andrew Morton April 30, 2021, 5:55 a.m. UTC

From: Yang Shi <[e-mail]>
Subject: mm: gup: remove FOLL_SPLIT

Since commit 5a52c9df62b4 ("uprobe: use FOLL_SPLIT_PMD instead of
FOLL_SPLIT") and commit ba925fa35057 ("s390/gmap: improve THP splitting")
FOLL_SPLIT has not been used anymore.  Remove the dead code.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Yang Shi <[e-mail]>
Reviewed-by: John Hubbard <[e-mail]>
Reviewed-by: Jason Gunthorpe <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 Documentation/vm/transhuge.rst |    5 -----
 include/linux/mm.h             |    1 -
 mm/gup.c                       |   28 ++--------------------------
 3 files changed, 2 insertions(+), 32 deletions(-)

Patch

--- a/Documentation/vm/transhuge.rst~mm-gup-remove-foll_split
+++ a/Documentation/vm/transhuge.rst
@@ -53,11 +53,6 @@  prevent the page from being split by any
    of handling GUP on hugetlbfs will also work fine on transparent
    hugepage backed mappings.
 
-In case you can't handle compound pages if they're returned by
-follow_page, the FOLL_SPLIT bit can be specified as a parameter to
-follow_page, so that it will split the hugepages before returning
-them.
-
 Graceful fallback
 =================
 
--- a/include/linux/mm.h~mm-gup-remove-foll_split
+++ a/include/linux/mm.h
@@ -2791,7 +2791,6 @@  struct page *follow_page(struct vm_area_
 #define FOLL_NOWAIT	0x20	/* if a disk transfer is needed, start the IO
 				 * and return without waiting upon it */
 #define FOLL_POPULATE	0x40	/* fault in page */
-#define FOLL_SPLIT	0x80	/* don't return transhuge pages, split them */
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
 #define FOLL_NUMA	0x200	/* force NUMA hinting page fault */
 #define FOLL_MIGRATION	0x400	/* wait for page to replace migration entry */
--- a/mm/gup.c~mm-gup-remove-foll_split
+++ a/mm/gup.c
@@ -516,18 +516,6 @@  retry:
 		}
 	}
 
-	if (flags & FOLL_SPLIT && PageTransCompound(page)) {
-		get_page(page);
-		pte_unmap_unlock(ptep, ptl);
-		lock_page(page);
-		ret = split_huge_page(page);
-		unlock_page(page);
-		put_page(page);
-		if (ret)
-			return ERR_PTR(ret);
-		goto retry;
-	}
-
 	/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
 	if (unlikely(!try_grab_page(page, flags))) {
 		page = ERR_PTR(-ENOMEM);
@@ -672,7 +660,7 @@  retry_locked:
 		spin_unlock(ptl);
 		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 	}
-	if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
+	if (flags & FOLL_SPLIT_PMD) {
 		int ret;
 		page = pmd_page(*pmd);
 		if (is_huge_zero_page(page)) {
@@ -681,19 +669,7 @@  retry_locked:
 			split_huge_pmd(vma, pmd, address);
 			if (pmd_trans_unstable(pmd))
 				ret = -EBUSY;
-		} else if (flags & FOLL_SPLIT) {
-			if (unlikely(!try_get_page(page))) {
-				spin_unlock(ptl);
-				return ERR_PTR(-ENOMEM);
-			}
-			spin_unlock(ptl);
-			lock_page(page);
-			ret = split_huge_page(page);
-			unlock_page(page);
-			put_page(page);
-			if (pmd_none(*pmd))
-				return no_page_table(vma, flags);
-		} else {  /* flags & FOLL_SPLIT_PMD */
+		} else {
 			spin_unlock(ptl);
 			split_huge_pmd(vma, pmd, address);
 			ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;