Re: [PATCH 1/2] mm: add support for discard of unused ptes
On Tue, 30 Jul 2013 13:44:22 -0700
Andrew Morton wrote:
> On Thu, 25 Jul 2013 10:54:20 +0200 Martin Schwidefsky
> wrote:
>
> > From: Konstantin Weitz
> >
> > In a virtualized environment and given an appropriate interface the guest
> > can mark pages as unused while they are free (for the s390 implementation
> > see git commit 45e576b1c3d00206 "guest page hinting light"). For the host
> > the unused state is a property of the pte.
> >
> > This patch adds the primitive 'pte_unused' and code to the host swap out
> > handler so that pages marked as unused by all mappers are not swapped out
> > but discarded instead, thus saving one IO for swap out and potentially
> > another one for swap in.
> >
> > ...
> >
> > --- a/include/asm-generic/pgtable.h
> > +++ b/include/asm-generic/pgtable.h
> > @@ -193,6 +193,19 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
> > }
> > #endif
> >
> > +#ifndef __HAVE_ARCH_PTE_UNUSED
> > +/*
> > + * Some architectures provide facilities to virtualization guests
> > + * so that they can flag allocated pages as unused. This allows the
> > + * host to transparently reclaim unused pages. This function returns
> > + * whether the pte's page is unused.
> > + */
> > +static inline int pte_unused(pte_t pte)
> > +{
> > + return 0;
> > +}
> > +#endif
> > +
> > #ifndef __HAVE_ARCH_PMD_SAME
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index cd356df..2291f25 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1234,6 +1234,16 @@ int try_to_unmap_one(struct page *page, struct
> > vm_area_struct *vma,
> > }
> > set_pte_at(mm, address, pte,
> >swp_entry_to_pte(make_hwpoison_entry(page)));
> > + } else if (pte_unused(pteval)) {
> > + /*
> > +* The guest indicated that the page content is of no
> > +* interest anymore. Simply discard the pte, vmscan
> > +* will take care of the rest.
> > +*/
> > + if (PageAnon(page))
> > + dec_mm_counter(mm, MM_ANONPAGES);
> > + else
> > + dec_mm_counter(mm, MM_FILEPAGES);
> > } else if (PageAnon(page)) {
> > swp_entry_t entry = { .val = page_private(page) };
>
> Obviously harmless. Please include this in whatever tree carries
> "[PATCH 2/2] s390/kvm: support collaborative memory management".
Cool, thanks. This will go out via the KVM tree then.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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Re: [PATCH 1/2] mm: add support for discard of unused ptes
On Thu, 25 Jul 2013 10:54:20 +0200 Martin Schwidefsky
wrote:
> From: Konstantin Weitz
>
> In a virtualized environment and given an appropriate interface the guest
> can mark pages as unused while they are free (for the s390 implementation
> see git commit 45e576b1c3d00206 "guest page hinting light"). For the host
> the unused state is a property of the pte.
>
> This patch adds the primitive 'pte_unused' and code to the host swap out
> handler so that pages marked as unused by all mappers are not swapped out
> but discarded instead, thus saving one IO for swap out and potentially
> another one for swap in.
>
> ...
>
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -193,6 +193,19 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
> }
> #endif
>
> +#ifndef __HAVE_ARCH_PTE_UNUSED
> +/*
> + * Some architectures provide facilities to virtualization guests
> + * so that they can flag allocated pages as unused. This allows the
> + * host to transparently reclaim unused pages. This function returns
> + * whether the pte's page is unused.
> + */
> +static inline int pte_unused(pte_t pte)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifndef __HAVE_ARCH_PMD_SAME
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> diff --git a/mm/rmap.c b/mm/rmap.c
> index cd356df..2291f25 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1234,6 +1234,16 @@ int try_to_unmap_one(struct page *page, struct
> vm_area_struct *vma,
> }
> set_pte_at(mm, address, pte,
> swp_entry_to_pte(make_hwpoison_entry(page)));
> + } else if (pte_unused(pteval)) {
> + /*
> + * The guest indicated that the page content is of no
> + * interest anymore. Simply discard the pte, vmscan
> + * will take care of the rest.
> + */
> + if (PageAnon(page))
> + dec_mm_counter(mm, MM_ANONPAGES);
> + else
> + dec_mm_counter(mm, MM_FILEPAGES);
> } else if (PageAnon(page)) {
> swp_entry_t entry = { .val = page_private(page) };
Obviously harmless. Please include this in whatever tree carries
"[PATCH 2/2] s390/kvm: support collaborative memory management".
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Re: [PATCH 1/2] mm: add support for discard of unused ptes
On 25/07/13 10:54, Martin Schwidefsky wrote:
> From: Konstantin Weitz
>
> In a virtualized environment and given an appropriate interface the guest
> can mark pages as unused while they are free (for the s390 implementation
> see git commit 45e576b1c3d00206 "guest page hinting light"). For the host
> the unused state is a property of the pte.
>
> This patch adds the primitive 'pte_unused' and code to the host swap out
> handler so that pages marked as unused by all mappers are not swapped out
> but discarded instead, thus saving one IO for swap out and potentially
> another one for swap in.
>
> [ Martin Schwidefsky: patch reordering and simplification ]
>
> Signed-off-by: Konstantin Weitz
> Signed-off-by: Martin Schwidefsky
Reviewed-by: Christian Borntraeger
> ---
> include/asm-generic/pgtable.h | 13 +
> mm/rmap.c | 10 ++
> 2 files changed, 23 insertions(+)
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 2f47ade..ec540c5 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -193,6 +193,19 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
> }
> #endif
>
> +#ifndef __HAVE_ARCH_PTE_UNUSED
> +/*
> + * Some architectures provide facilities to virtualization guests
> + * so that they can flag allocated pages as unused. This allows the
> + * host to transparently reclaim unused pages. This function returns
> + * whether the pte's page is unused.
> + */
> +static inline int pte_unused(pte_t pte)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifndef __HAVE_ARCH_PMD_SAME
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
> diff --git a/mm/rmap.c b/mm/rmap.c
> index cd356df..2291f25 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1234,6 +1234,16 @@ int try_to_unmap_one(struct page *page, struct
> vm_area_struct *vma,
> }
> set_pte_at(mm, address, pte,
> swp_entry_to_pte(make_hwpoison_entry(page)));
> + } else if (pte_unused(pteval)) {
> + /*
> + * The guest indicated that the page content is of no
> + * interest anymore. Simply discard the pte, vmscan
> + * will take care of the rest.
> + */
> + if (PageAnon(page))
> + dec_mm_counter(mm, MM_ANONPAGES);
> + else
> + dec_mm_counter(mm, MM_FILEPAGES);
> } else if (PageAnon(page)) {
> swp_entry_t entry = { .val = page_private(page) };
>
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[PATCH 1/2] mm: add support for discard of unused ptes
From: Konstantin Weitz
In a virtualized environment and given an appropriate interface the guest
can mark pages as unused while they are free (for the s390 implementation
see git commit 45e576b1c3d00206 "guest page hinting light"). For the host
the unused state is a property of the pte.
This patch adds the primitive 'pte_unused' and code to the host swap out
handler so that pages marked as unused by all mappers are not swapped out
but discarded instead, thus saving one IO for swap out and potentially
another one for swap in.
[ Martin Schwidefsky: patch reordering and simplification ]
Signed-off-by: Konstantin Weitz
Signed-off-by: Martin Schwidefsky
---
include/asm-generic/pgtable.h | 13 +
mm/rmap.c | 10 ++
2 files changed, 23 insertions(+)
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 2f47ade..ec540c5 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -193,6 +193,19 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
}
#endif
+#ifndef __HAVE_ARCH_PTE_UNUSED
+/*
+ * Some architectures provide facilities to virtualization guests
+ * so that they can flag allocated pages as unused. This allows the
+ * host to transparently reclaim unused pages. This function returns
+ * whether the pte's page is unused.
+ */
+static inline int pte_unused(pte_t pte)
+{
+ return 0;
+}
+#endif
+
#ifndef __HAVE_ARCH_PMD_SAME
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
diff --git a/mm/rmap.c b/mm/rmap.c
index cd356df..2291f25 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1234,6 +1234,16 @@ int try_to_unmap_one(struct page *page, struct
vm_area_struct *vma,
}
set_pte_at(mm, address, pte,
swp_entry_to_pte(make_hwpoison_entry(page)));
+ } else if (pte_unused(pteval)) {
+ /*
+* The guest indicated that the page content is of no
+* interest anymore. Simply discard the pte, vmscan
+* will take care of the rest.
+*/
+ if (PageAnon(page))
+ dec_mm_counter(mm, MM_ANONPAGES);
+ else
+ dec_mm_counter(mm, MM_FILEPAGES);
} else if (PageAnon(page)) {
swp_entry_t entry = { .val = page_private(page) };
--
1.7.9.5
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