| Message ID | 20220506072502.2177828-5-Penny.Zheng@arm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | static shared memory on dom0less system | expand |
On Fri, 6 May 2022, Penny Zheng wrote: > Later, we need to add the right amount of references, which should be > the number of borrower domains, to the owner domain. Since we only have > get_page() to increment the page reference by 1, a loop is needed per > page, which is inefficient and time-consuming. > > To save the loop time, this commit introduces a set of new helpers > put_page_nr() and get_page_nr() to increment/drop the page reference by nr. > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> > --- > v2 change: > - new commit > --- > xen/arch/arm/include/asm/mm.h | 4 ++++ > xen/arch/arm/mm.c | 36 +++++++++++++++++++++++++---------- > 2 files changed, 30 insertions(+), 10 deletions(-) > > diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h > index 424aaf2823..c737d51e4d 100644 > --- a/xen/arch/arm/include/asm/mm.h > +++ b/xen/arch/arm/include/asm/mm.h > @@ -347,6 +347,10 @@ void free_init_memory(void); > int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn, > unsigned int order); > > +extern bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr); > +extern void put_page_nr(struct page_info *page, unsigned long nr); > + > extern void put_page_type(struct page_info *page); > static inline void put_page_and_type(struct page_info *page) > { > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c > index 7b1f2f4906..e565979f3c 100644 > --- a/xen/arch/arm/mm.c > +++ b/xen/arch/arm/mm.c > @@ -1537,7 +1537,8 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg) > return 0; > } > > -struct domain *page_get_owner_and_reference(struct page_info *page) > +static struct domain *page_get_owner_and_nr_reference(struct page_info *page, > + unsigned long nr) > { > unsigned long x, y = page->count_info; > struct domain *owner; > @@ -1545,13 +1546,14 @@ struct domain *page_get_owner_and_reference(struct page_info *page) > do { > x = y; > /* > + * Consider the minimum case(nr = 1): > * Count == 0: Page is not allocated, so we cannot take a reference. > * Count == -1: Reference count would wrap, which is invalid. > */ > if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) > return NULL; > } > - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); > + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); > > owner = page_get_owner(page); > ASSERT(owner); > @@ -1559,36 +1561,50 @@ struct domain *page_get_owner_and_reference(struct page_info *page) > return owner; > } > > -void put_page(struct page_info *page) > +struct domain *page_get_owner_and_reference(struct page_info *page) > +{ > + return page_get_owner_and_nr_reference(page, 1); > +} > + > +void put_page_nr(struct page_info *page, unsigned long nr) > { > unsigned long nx, x, y = page->count_info; > > do { > - ASSERT((y & PGC_count_mask) != 0); > + ASSERT(((y - nr) & PGC_count_mask) >= 0); Why this change? The original ASSERT is to check that we enter the loop only when count_info is greater than 0. It should still apply even for put_page_nr without modifications? > x = y; > - nx = x - 1; > + nx = x - nr; > } > while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); > > if ( unlikely((nx & PGC_count_mask) == 0) ) > - { > free_domheap_page(page); > - } > } > > -bool get_page(struct page_info *page, const struct domain *domain) > +void put_page(struct page_info *page) > { > - const struct domain *owner = page_get_owner_and_reference(page); > + put_page_nr(page, 1); > +} > + > +bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr) > +{ > + const struct domain *owner = page_get_owner_and_nr_reference(page, nr); > > if ( likely(owner == domain) ) > return true; > > if ( owner != NULL ) > - put_page(page); > + put_page_nr(page, nr); > > return false; > } > > +bool get_page(struct page_info *page, const struct domain *domain) > +{ > + return get_page_nr(page, domain, 1); > +} > + > /* Common code requires get_page_type and put_page_type. > * We don't care about typecounts so we just do the minimum to make it > * happy. */ > -- > 2.25.1 >
Hi Stefano > -----Original Message----- > From: Stefano Stabellini <sstabellini@kernel.org> > Sent: Saturday, May 7, 2022 9:09 AM > To: Penny Zheng <Penny.Zheng@arm.com> > Cc: xen-devel@lists.xenproject.org; Wei Chen <Wei.Chen@arm.com>; Stefano > Stabellini <sstabellini@kernel.org>; Julien Grall <julien@xen.org>; Bertrand > Marquis <Bertrand.Marquis@arm.com>; Volodymyr Babchuk > <Volodymyr_Babchuk@epam.com> > Subject: Re: [PATCH v2 4/9] xen/arm: introduce put_page_nr and get_page_nr > > On Fri, 6 May 2022, Penny Zheng wrote: > > Later, we need to add the right amount of references, which should be > > the number of borrower domains, to the owner domain. Since we only > > have > > get_page() to increment the page reference by 1, a loop is needed per > > page, which is inefficient and time-consuming. > > > > To save the loop time, this commit introduces a set of new helpers > > put_page_nr() and get_page_nr() to increment/drop the page reference by > nr. > > > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> > > --- > > v2 change: > > - new commit > > --- > > xen/arch/arm/include/asm/mm.h | 4 ++++ > > xen/arch/arm/mm.c | 36 +++++++++++++++++++++++++---------- > > 2 files changed, 30 insertions(+), 10 deletions(-) > > > > diff --git a/xen/arch/arm/include/asm/mm.h > > b/xen/arch/arm/include/asm/mm.h index 424aaf2823..c737d51e4d 100644 > > --- a/xen/arch/arm/include/asm/mm.h > > +++ b/xen/arch/arm/include/asm/mm.h > > @@ -347,6 +347,10 @@ void free_init_memory(void); int > > guest_physmap_mark_populate_on_demand(struct domain *d, unsigned > long gfn, > > unsigned int order); > > > > +extern bool get_page_nr(struct page_info *page, const struct domain > *domain, > > + unsigned long nr); extern void > > +put_page_nr(struct page_info *page, unsigned long nr); > > + > > extern void put_page_type(struct page_info *page); static inline > > void put_page_and_type(struct page_info *page) { diff --git > > a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 7b1f2f4906..e565979f3c > > 100644 > > --- a/xen/arch/arm/mm.c > > +++ b/xen/arch/arm/mm.c > > @@ -1537,7 +1537,8 @@ long arch_memory_op(int op, > XEN_GUEST_HANDLE_PARAM(void) arg) > > return 0; > > } > > > > -struct domain *page_get_owner_and_reference(struct page_info *page) > > +static struct domain *page_get_owner_and_nr_reference(struct page_info > *page, > > + unsigned long > > +nr) > > { > > unsigned long x, y = page->count_info; > > struct domain *owner; > > @@ -1545,13 +1546,14 @@ struct domain > *page_get_owner_and_reference(struct page_info *page) > > do { > > x = y; > > /* > > + * Consider the minimum case(nr = 1): > > * Count == 0: Page is not allocated, so we cannot take a reference. > > * Count == -1: Reference count would wrap, which is invalid. > > */ > > if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) > > return NULL; > > } > > - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); > > + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); > > > > owner = page_get_owner(page); > > ASSERT(owner); > > @@ -1559,36 +1561,50 @@ struct domain > *page_get_owner_and_reference(struct page_info *page) > > return owner; > > } > > > > -void put_page(struct page_info *page) > > +struct domain *page_get_owner_and_reference(struct page_info *page) { > > + return page_get_owner_and_nr_reference(page, 1); } > > + > > +void put_page_nr(struct page_info *page, unsigned long nr) > > { > > unsigned long nx, x, y = page->count_info; > > > > do { > > - ASSERT((y & PGC_count_mask) != 0); > > + ASSERT(((y - nr) & PGC_count_mask) >= 0); > > Why this change? The original ASSERT is to check that we enter the loop only > when count_info is greater than 0. It should still apply even for put_page_nr > without modifications? > > Oh, I understand wrongly about the ASSERT. I thought it was to check the result count_info after the loop will be not smaller than 0. Do you think we still need to ensure that? Maybe ASSERT( ((y & PGC_count_mask) != 0) && (((y - nr) & PGC_count_mask) >= 0)); ? > > > x = y; > > - nx = x - 1; > > + nx = x - nr; > > } > > while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); > > > > if ( unlikely((nx & PGC_count_mask) == 0) ) > > - { > > free_domheap_page(page); > > - } > > } > > > > -bool get_page(struct page_info *page, const struct domain *domain) > > +void put_page(struct page_info *page) > > { > > - const struct domain *owner = page_get_owner_and_reference(page); > > + put_page_nr(page, 1); > > +} > > + > > +bool get_page_nr(struct page_info *page, const struct domain *domain, > > + unsigned long nr) > > +{ > > + const struct domain *owner = > > +page_get_owner_and_nr_reference(page, nr); > > > > if ( likely(owner == domain) ) > > return true; > > > > if ( owner != NULL ) > > - put_page(page); > > + put_page_nr(page, nr); > > > > return false; > > } > > > > +bool get_page(struct page_info *page, const struct domain *domain) { > > + return get_page_nr(page, domain, 1); } > > + > > /* Common code requires get_page_type and put_page_type. > > * We don't care about typecounts so we just do the minimum to make it > > * happy. */ > > -- > > 2.25.1 > >
Hi Penny, On 06/05/2022 08:24, Penny Zheng wrote: > Later, we need to add the right amount of references, which should be > the number of borrower domains, to the owner domain. Since we only have > get_page() to increment the page reference by 1, a loop is needed per > page, which is inefficient and time-consuming. > > To save the loop time, this commit introduces a set of new helpers > put_page_nr() and get_page_nr() to increment/drop the page reference by nr. > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> > --- > v2 change: > - new commit > --- > xen/arch/arm/include/asm/mm.h | 4 ++++ > xen/arch/arm/mm.c | 36 +++++++++++++++++++++++++---------- > 2 files changed, 30 insertions(+), 10 deletions(-) > > diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h > index 424aaf2823..c737d51e4d 100644 > --- a/xen/arch/arm/include/asm/mm.h > +++ b/xen/arch/arm/include/asm/mm.h > @@ -347,6 +347,10 @@ void free_init_memory(void); > int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn, > unsigned int order); > > +extern bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr); > +extern void put_page_nr(struct page_info *page, unsigned long nr); > + > extern void put_page_type(struct page_info *page); > static inline void put_page_and_type(struct page_info *page) > { > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c > index 7b1f2f4906..e565979f3c 100644 > --- a/xen/arch/arm/mm.c > +++ b/xen/arch/arm/mm.c > @@ -1537,7 +1537,8 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg) > return 0; > } > > -struct domain *page_get_owner_and_reference(struct page_info *page) > +static struct domain *page_get_owner_and_nr_reference(struct page_info *page, > + unsigned long nr) > { > unsigned long x, y = page->count_info; > struct domain *owner; > @@ -1545,13 +1546,14 @@ struct domain *page_get_owner_and_reference(struct page_info *page) > do { > x = y; > /* > + * Consider the minimum case(nr = 1): > * Count == 0: Page is not allocated, so we cannot take a reference. > * Count == -1: Reference count would wrap, which is invalid. > */ > if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) Shouldn't this be updated to check overflow with "n"? > return NULL; > } > - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); > + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); > > owner = page_get_owner(page); > ASSERT(owner); > @@ -1559,36 +1561,50 @@ struct domain *page_get_owner_and_reference(struct page_info *page) > return owner; > } > > -void put_page(struct page_info *page) > +struct domain *page_get_owner_and_reference(struct page_info *page) > +{ > + return page_get_owner_and_nr_reference(page, 1); > +} > + > +void put_page_nr(struct page_info *page, unsigned long nr) > { > unsigned long nx, x, y = page->count_info; > > do { > - ASSERT((y & PGC_count_mask) != 0); > + ASSERT(((y - nr) & PGC_count_mask) >= 0); > x = y; > - nx = x - 1; > + nx = x - nr; > } > while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); > > if ( unlikely((nx & PGC_count_mask) == 0) ) > - { > free_domheap_page(page); > - } Sounds like a spurious change. > } > > -bool get_page(struct page_info *page, const struct domain *domain) > +void put_page(struct page_info *page) > { > - const struct domain *owner = page_get_owner_and_reference(page); > + put_page_nr(page, 1); > +} > + > +bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr) > +{ > + const struct domain *owner = page_get_owner_and_nr_reference(page, nr); > > if ( likely(owner == domain) ) > return true; > > if ( owner != NULL ) > - put_page(page); > + put_page_nr(page, nr); > > return false; > } > > +bool get_page(struct page_info *page, const struct domain *domain) > +{ > + return get_page_nr(page, domain, 1); > +} > + > /* Common code requires get_page_type and put_page_type. > * We don't care about typecounts so we just do the minimum to make it > * happy. */ Cheers,
On Sat, 7 May 2022, Penny Zheng wrote: > > On Fri, 6 May 2022, Penny Zheng wrote: > > > Later, we need to add the right amount of references, which should be > > > the number of borrower domains, to the owner domain. Since we only > > > have > > > get_page() to increment the page reference by 1, a loop is needed per > > > page, which is inefficient and time-consuming. > > > > > > To save the loop time, this commit introduces a set of new helpers > > > put_page_nr() and get_page_nr() to increment/drop the page reference by > > nr. > > > > > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> > > > --- > > > v2 change: > > > - new commit > > > --- > > > xen/arch/arm/include/asm/mm.h | 4 ++++ > > > xen/arch/arm/mm.c | 36 +++++++++++++++++++++++++---------- > > > 2 files changed, 30 insertions(+), 10 deletions(-) > > > > > > diff --git a/xen/arch/arm/include/asm/mm.h > > > b/xen/arch/arm/include/asm/mm.h index 424aaf2823..c737d51e4d 100644 > > > --- a/xen/arch/arm/include/asm/mm.h > > > +++ b/xen/arch/arm/include/asm/mm.h > > > @@ -347,6 +347,10 @@ void free_init_memory(void); int > > > guest_physmap_mark_populate_on_demand(struct domain *d, unsigned > > long gfn, > > > unsigned int order); > > > > > > +extern bool get_page_nr(struct page_info *page, const struct domain > > *domain, > > > + unsigned long nr); extern void > > > +put_page_nr(struct page_info *page, unsigned long nr); > > > + > > > extern void put_page_type(struct page_info *page); static inline > > > void put_page_and_type(struct page_info *page) { diff --git > > > a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 7b1f2f4906..e565979f3c > > > 100644 > > > --- a/xen/arch/arm/mm.c > > > +++ b/xen/arch/arm/mm.c > > > @@ -1537,7 +1537,8 @@ long arch_memory_op(int op, > > XEN_GUEST_HANDLE_PARAM(void) arg) > > > return 0; > > > } > > > > > > -struct domain *page_get_owner_and_reference(struct page_info *page) > > > +static struct domain *page_get_owner_and_nr_reference(struct page_info > > *page, > > > + unsigned long > > > +nr) > > > { > > > unsigned long x, y = page->count_info; > > > struct domain *owner; > > > @@ -1545,13 +1546,14 @@ struct domain > > *page_get_owner_and_reference(struct page_info *page) > > > do { > > > x = y; > > > /* > > > + * Consider the minimum case(nr = 1): > > > * Count == 0: Page is not allocated, so we cannot take a reference. > > > * Count == -1: Reference count would wrap, which is invalid. > > > */ > > > if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) > > > return NULL; > > > } > > > - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); > > > + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); > > > > > > owner = page_get_owner(page); > > > ASSERT(owner); > > > @@ -1559,36 +1561,50 @@ struct domain > > *page_get_owner_and_reference(struct page_info *page) > > > return owner; > > > } > > > > > > -void put_page(struct page_info *page) > > > +struct domain *page_get_owner_and_reference(struct page_info *page) { > > > + return page_get_owner_and_nr_reference(page, 1); } > > > + > > > +void put_page_nr(struct page_info *page, unsigned long nr) > > > { > > > unsigned long nx, x, y = page->count_info; > > > > > > do { > > > - ASSERT((y & PGC_count_mask) != 0); > > > + ASSERT(((y - nr) & PGC_count_mask) >= 0); > > > > Why this change? The original ASSERT is to check that we enter the loop only > > when count_info is greater than 0. It should still apply even for put_page_nr > > without modifications? > > > > > > Oh, I understand wrongly about the ASSERT. I thought it was to > check the result count_info after the loop will be not smaller than 0. > > Do you think we still need to ensure that? Maybe ASSERT( ((y & PGC_count_mask) != 0) && (((y - nr) & PGC_count_mask) >= 0)); ? I think it should be: ASSERT((y & PGC_count_mask) >= nr);
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h index 424aaf2823..c737d51e4d 100644 --- a/xen/arch/arm/include/asm/mm.h +++ b/xen/arch/arm/include/asm/mm.h @@ -347,6 +347,10 @@ void free_init_memory(void); int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn, unsigned int order); +extern bool get_page_nr(struct page_info *page, const struct domain *domain, + unsigned long nr); +extern void put_page_nr(struct page_info *page, unsigned long nr); + extern void put_page_type(struct page_info *page); static inline void put_page_and_type(struct page_info *page) { diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 7b1f2f4906..e565979f3c 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -1537,7 +1537,8 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg) return 0; } -struct domain *page_get_owner_and_reference(struct page_info *page) +static struct domain *page_get_owner_and_nr_reference(struct page_info *page, + unsigned long nr) { unsigned long x, y = page->count_info; struct domain *owner; @@ -1545,13 +1546,14 @@ struct domain *page_get_owner_and_reference(struct page_info *page) do { x = y; /* + * Consider the minimum case(nr = 1): * Count == 0: Page is not allocated, so we cannot take a reference. * Count == -1: Reference count would wrap, which is invalid. */ if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) return NULL; } - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); owner = page_get_owner(page); ASSERT(owner); @@ -1559,36 +1561,50 @@ struct domain *page_get_owner_and_reference(struct page_info *page) return owner; } -void put_page(struct page_info *page) +struct domain *page_get_owner_and_reference(struct page_info *page) +{ + return page_get_owner_and_nr_reference(page, 1); +} + +void put_page_nr(struct page_info *page, unsigned long nr) { unsigned long nx, x, y = page->count_info; do { - ASSERT((y & PGC_count_mask) != 0); + ASSERT(((y - nr) & PGC_count_mask) >= 0); x = y; - nx = x - 1; + nx = x - nr; } while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); if ( unlikely((nx & PGC_count_mask) == 0) ) - { free_domheap_page(page); - } } -bool get_page(struct page_info *page, const struct domain *domain) +void put_page(struct page_info *page) { - const struct domain *owner = page_get_owner_and_reference(page); + put_page_nr(page, 1); +} + +bool get_page_nr(struct page_info *page, const struct domain *domain, + unsigned long nr) +{ + const struct domain *owner = page_get_owner_and_nr_reference(page, nr); if ( likely(owner == domain) ) return true; if ( owner != NULL ) - put_page(page); + put_page_nr(page, nr); return false; } +bool get_page(struct page_info *page, const struct domain *domain) +{ + return get_page_nr(page, domain, 1); +} + /* Common code requires get_page_type and put_page_type. * We don't care about typecounts so we just do the minimum to make it * happy. */
Later, we need to add the right amount of references, which should be the number of borrower domains, to the owner domain. Since we only have get_page() to increment the page reference by 1, a loop is needed per page, which is inefficient and time-consuming. To save the loop time, this commit introduces a set of new helpers put_page_nr() and get_page_nr() to increment/drop the page reference by nr. Signed-off-by: Penny Zheng <penny.zheng@arm.com> --- v2 change: - new commit --- xen/arch/arm/include/asm/mm.h | 4 ++++ xen/arch/arm/mm.c | 36 +++++++++++++++++++++++++---------- 2 files changed, 30 insertions(+), 10 deletions(-)