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authorLinus Torvalds <torvalds@linux-foundation.org>2008-06-20 14:18:25 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-06-20 14:18:25 -0400
commit89f5b7da2a6bad2e84670422ab8192382a5aeb9f (patch)
tree4f55cf9ef8a76d4b9a960e1b443ed015e63e713f /mm/migrate.c
parent9bedbcb207ed9a571b239231d99c8fd4a34ae24d (diff)
Reinstate ZERO_PAGE optimization in 'get_user_pages()' and fix XIP
KAMEZAWA Hiroyuki and Oleg Nesterov point out that since the commit 557ed1fa2620dc119adb86b34c614e152a629a80 ("remove ZERO_PAGE") removed the ZERO_PAGE from the VM mappings, any users of get_user_pages() will generally now populate the VM with real empty pages needlessly. We used to get the ZERO_PAGE when we did the "handle_mm_fault()", but since fault handling no longer uses ZERO_PAGE for new anonymous pages, we now need to handle that special case in follow_page() instead. In particular, the removal of ZERO_PAGE effectively removed the core file writing optimization where we would skip writing pages that had not been populated at all, and increased memory pressure a lot by allocating all those useless newly zeroed pages. This reinstates the optimization by making the unmapped PTE case the same as for a non-existent page table, which already did this correctly. While at it, this also fixes the XIP case for follow_page(), where the caller could not differentiate between the case of a page that simply could not be used (because it had no "struct page" associated with it) and a page that just wasn't mapped. We do that by simply returning an error pointer for pages that could not be turned into a "struct page *". The error is arbitrarily picked to be EFAULT, since that was what get_user_pages() already used for the equivalent IO-mapped page case. [ Also removed an impossible test for pte_offset_map_lock() failing: that's not how that function works ] Acked-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Nick Piggin <npiggin@suse.de> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/migrate.c')
-rw-r--r--mm/migrate.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 449d77d409f5..112bcaeaa104 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -865,6 +865,11 @@ static int do_move_pages(struct mm_struct *mm, struct page_to_node *pm,
865 goto set_status; 865 goto set_status;
866 866
867 page = follow_page(vma, pp->addr, FOLL_GET); 867 page = follow_page(vma, pp->addr, FOLL_GET);
868
869 err = PTR_ERR(page);
870 if (IS_ERR(page))
871 goto set_status;
872
868 err = -ENOENT; 873 err = -ENOENT;
869 if (!page) 874 if (!page)
870 goto set_status; 875 goto set_status;
@@ -928,6 +933,11 @@ static int do_pages_stat(struct mm_struct *mm, struct page_to_node *pm)
928 goto set_status; 933 goto set_status;
929 934
930 page = follow_page(vma, pm->addr, 0); 935 page = follow_page(vma, pm->addr, 0);
936
937 err = PTR_ERR(page);
938 if (IS_ERR(page))
939 goto set_status;
940
931 err = -ENOENT; 941 err = -ENOENT;
932 /* Use PageReserved to check for zero page */ 942 /* Use PageReserved to check for zero page */
933 if (!page || PageReserved(page)) 943 if (!page || PageReserved(page))