The patch titled
improve ZERO_PAGE handling in follow_page()
has been removed from the -mm tree. Its filename was
improve-zero_page-handling-in-follow_page.patch
This patch was dropped because compilation failed. Please redo and resend
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: improve ZERO_PAGE handling in follow_page()
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
follow_page() is called from get_user_pages(), which returns specified user
page.
follow_page() can return 1) a page or 2) NULL or 3)ZERO_PAGE.
If NULL, handle_mm_fault() is called.
Now, follow_page() to unused pte returns NULL if page table exists. As a
result get_user_pages() calls handle_mm_fault() and allocate new memory. This
behavior increases memory consumption at coredump, which does
read-once-but-never-written page fault. By returning ZERO_PAGE() against
READ/ANON request, we can avoid it.
(Because exec's arguments copy needs to call handle_mm_fault at WRITE/ANON
request, we just handle READ/ANON case here.)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Tested-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>
Acked-by: Nick Piggin <npiggin@xxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff -puN mm/memory.c~improve-zero_page-handling-in-follow_page mm/memory.c
--- a/mm/memory.c~improve-zero_page-handling-in-follow_page
+++ a/mm/memory.c
@@ -992,15 +992,15 @@ struct page *follow_page(struct vm_area_
page = NULL;
pgd = pgd_offset(mm, address);
if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
- goto no_page_table;
+ goto null_or_zeropage;
pud = pud_offset(pgd, address);
if (pud_none(*pud) || unlikely(pud_bad(*pud)))
- goto no_page_table;
+ goto null_or_zeropage;
pmd = pmd_offset(pud, address);
if (pmd_none(*pmd))
- goto no_page_table;
+ goto null_or_zeropage;
if (pmd_huge(*pmd)) {
BUG_ON(flags & FOLL_GET);
@@ -1016,8 +1016,14 @@ struct page *follow_page(struct vm_area_
goto out;
pte = *ptep;
- if (!pte_present(pte))
+ if (!pte_present(pte)) {
+ /* Read fault to empty pte can return ZERO_PAGE */
+ if (!(flags & FOLL_WRITE) && pte_none(pte)) {
+ pte_unmap_unlock(ptep, ptl);
+ goto null_or_zeropage;
+ }
goto unlock;
+ }
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
page = vm_normal_page(vma, address, pte);
@@ -1037,7 +1043,7 @@ unlock:
out:
return page;
-no_page_table:
+null_or_zeropage:
/*
* When core dumping an enormous anonymous area that nobody
* has touched so far, we don't want to allocate page tables.
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
memcg-fix-possible-panic-when-config_mm_owner=y.patch
memcg-fix-possible-panic-when-config_mm_owner=y-checkpatch-fixes.patch
cgroups-fix-documentation.patch
improve-zero_page-handling-in-follow_page.patch
mark-res_counter_charge_locked-with-__must_check.patch
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