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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 /arch
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 'arch')
-rw-r--r--arch/powerpc/kernel/vdso.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index c21a626af676..ce245a850db2 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -142,7 +142,7 @@ static void dump_one_vdso_page(struct page *pg, struct page *upg)
142 printk("kpg: %p (c:%d,f:%08lx)", __va(page_to_pfn(pg) << PAGE_SHIFT), 142 printk("kpg: %p (c:%d,f:%08lx)", __va(page_to_pfn(pg) << PAGE_SHIFT),
143 page_count(pg), 143 page_count(pg),
144 pg->flags); 144 pg->flags);
145 if (upg/* && pg != upg*/) { 145 if (upg && !IS_ERR(upg) /* && pg != upg*/) {
146 printk(" upg: %p (c:%d,f:%08lx)", __va(page_to_pfn(upg) 146 printk(" upg: %p (c:%d,f:%08lx)", __va(page_to_pfn(upg)
147 << PAGE_SHIFT), 147 << PAGE_SHIFT),
148 page_count(upg), 148 page_count(upg),