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Date: Fri, 11 Nov 2011 14:36:29 +0800
From: Shaohua Li <shaohua.li@...el.com>
To: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>, linux-mm <linux-mm@...ck.org>,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch 3/5]thp: add tlb_remove_pmd_tlb_entry
On Thu, 2011-11-10 at 23:36 +0800, Andrea Arcangeli wrote:
> On Tue, Oct 25, 2011 at 10:59:31AM +0800, Shaohua Li wrote:
> > Index: linux/arch/x86/include/asm/tlb.h
> > ===================================================================
> > --- linux.orig/arch/x86/include/asm/tlb.h 2011-10-25 09:00:39.000000000 +0800
> > +++ linux/arch/x86/include/asm/tlb.h 2011-10-25 09:02:52.000000000 +0800
> > @@ -4,6 +4,7 @@
> > #define tlb_start_vma(tlb, vma) do { } while (0)
> > #define tlb_end_vma(tlb, vma) do { } while (0)
> > #define __tlb_remove_tlb_entry(tlb, ptep, address) do { } while (0)
> > +#define __tlb_remove_pmd_tlb_entry(tlb, pmdp, address) do { } while (0)
> > #define tlb_flush(tlb) flush_tlb_mm((tlb)->mm)
>
> This is superfluous, it's already define below as noop.
>
> >
> > #include <asm-generic/tlb.h>
> > Index: linux/include/asm-generic/tlb.h
> > ===================================================================
> > --- linux.orig/include/asm-generic/tlb.h 2011-10-25 09:00:23.000000000 +0800
> > +++ linux/include/asm-generic/tlb.h 2011-10-25 09:18:01.000000000 +0800
> > @@ -139,6 +139,16 @@ static inline void tlb_remove_page(struc
> > __tlb_remove_tlb_entry(tlb, ptep, address); \
> > } while (0)
> >
> > +#ifndef __tlb_remove_pmd_tlb_entry
> > +#define __tlb_remove_pmd_tlb_entry(tlb, pmdp, address) do {} while(0)
> > +#endif
> > +
> > +#define tlb_remove_pmd_tlb_entry(tlb, pmdp, address) \
> > + do { \
> > + tlb->need_flush = 1; \
> > + __tlb_remove_pmd_tlb_entry(tlb, pmdp, address); \
> > + } while (0)
>
> this looks weird, why do we set need_flush = 1 again, considering that
> we're doing tlb_remove_page() just a few lines later (which also sets
> tlb->need_flush = 1).
>
> Ok that other archs may need the __tlb_remove_pmd_tlb_entry to be
> called (and I've no idea why), but the need_flush = 1 seems
> unnecessary.
>
> Why other archs need the __tlb_remove_pmd_tlb_entry to be called?
>
> One way to go would be to change the tlb->need_flush = 1 in
> __tlb_remove_page to a VM_BUG_ON(!tlb->need_flush) and then we keep it
> above and we add the __tlb_remove_pmd_tlb_entry call.
>
> Or is there any place where __tlb_remove_page is called without a
> tlb_remove_*tlb_entry being called before it?
>
> In any case the VM_BUG_ON will verify this.
ok, I made the whole tlb_remove_pmd_tlb_entry() noop now. we don't need
add anything on it for x86 currently. We can change it later if
necessary.
We have tlb_remove_tlb_entry to indicate a pte tlb flush entry should be
flushed, but not a corresponding API for pmd entry. This isn't a problem so far
because THP is only for x86 currently and tlb_flush() under x86 will flush
entire TLB. But this is confusion and could be missed if thp is ported to
other arch.
Signed-off-by: Shaohua Li <shaohua.li@...el.com>
---
include/asm-generic/tlb.h | 6 ++++++
include/linux/huge_mm.h | 2 +-
mm/huge_memory.c | 3 ++-
mm/memory.c | 2 +-
4 files changed, 10 insertions(+), 3 deletions(-)
Index: linux/include/asm-generic/tlb.h
===================================================================
--- linux.orig/include/asm-generic/tlb.h 2011-11-11 14:26:33.000000000 +0800
+++ linux/include/asm-generic/tlb.h 2011-11-11 14:26:35.000000000 +0800
@@ -139,6 +139,12 @@ static inline void tlb_remove_page(struc
__tlb_remove_tlb_entry(tlb, ptep, address); \
} while (0)
+/**
+ * tlb_remove_pmd_tlb_entry - remember a pmd mapping for later tlb invalidation
+ * This is a nop so far, because only x86 needs it.
+ */
+#define tlb_remove_pmd_tlb_entry(tlb, pmdp, address) do {} while (0)
+
#define pte_free_tlb(tlb, ptep, address) \
do { \
tlb->need_flush = 1; \
Index: linux/include/linux/huge_mm.h
===================================================================
--- linux.orig/include/linux/huge_mm.h 2011-11-11 14:26:33.000000000 +0800
+++ linux/include/linux/huge_mm.h 2011-11-11 14:26:35.000000000 +0800
@@ -18,7 +18,7 @@ extern struct page *follow_trans_huge_pm
unsigned int flags);
extern int zap_huge_pmd(struct mmu_gather *tlb,
struct vm_area_struct *vma,
- pmd_t *pmd);
+ pmd_t *pmd, unsigned long addr);
extern int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
unsigned char *vec);
Index: linux/mm/huge_memory.c
===================================================================
--- linux.orig/mm/huge_memory.c 2011-11-11 14:26:33.000000000 +0800
+++ linux/mm/huge_memory.c 2011-11-11 14:26:35.000000000 +0800
@@ -1026,7 +1026,7 @@ out:
}
int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
- pmd_t *pmd)
+ pmd_t *pmd, unsigned long addr)
{
int ret = 0;
@@ -1042,6 +1042,7 @@ int zap_huge_pmd(struct mmu_gather *tlb,
pgtable = get_pmd_huge_pte(tlb->mm);
page = pmd_page(*pmd);
pmd_clear(pmd);
+ tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
page_remove_rmap(page);
VM_BUG_ON(page_mapcount(page) < 0);
add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
Index: linux/mm/memory.c
===================================================================
--- linux.orig/mm/memory.c 2011-11-11 14:26:33.000000000 +0800
+++ linux/mm/memory.c 2011-11-11 14:26:35.000000000 +0800
@@ -1231,7 +1231,7 @@ static inline unsigned long zap_pmd_rang
if (next-addr != HPAGE_PMD_SIZE) {
VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem));
split_huge_page_pmd(vma->vm_mm, pmd);
- } else if (zap_huge_pmd(tlb, vma, pmd))
+ } else if (zap_huge_pmd(tlb, vma, pmd, addr))
continue;
/* fall through */
}
--
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