Re: [PATCH v3 1/3] mm/memblock: introduce a new helper memblock_estimated_nr_pages()

[Oleg Nesterov <oleg@redhat.com>]

As I have already said, I can't review this patch.

But I am curious, why set_max_threads() is the only user of the new helper?
Say, should files_maxfiles_init() use it too or not? Perhaps the changelog
can explain this?

Thanks,

Oleg.

On 07/07, David Hildenbrand wrote:
>
> On 06.07.24 03:28, Wei Yang wrote:
> >On Fri, Jul 05, 2024 at 12:09:48PM +0300, Mike Rapoport wrote:
> >>On Wed, Jul 03, 2024 at 12:51:49AM +0000, Wei Yang wrote:
> >>>Instead of using raw memblock api, we wrap a new helper for user.
> >>
> >>The changelog should be more elaborate and explain why this function is
> >>needed.
> >>
> >>>Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> >>>---
> >>>  include/linux/memblock.h |  1 +
> >>>  mm/memblock.c            | 19 +++++++++++++++++++
> >>>  2 files changed, 20 insertions(+)
> >>>
> >>>diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> >>>index 40c62aca36ec..7d1c32b3dc12 100644
> >>>--- a/include/linux/memblock.h
> >>>+++ b/include/linux/memblock.h
> >>>@@ -486,6 +486,7 @@ static inline __init_memblock bool memblock_bottom_up(void)
> >>>  phys_addr_t memblock_phys_mem_size(void);
> >>>  phys_addr_t memblock_reserved_size(void);
> >>>+unsigned long memblock_estimated_nr_pages(void);
> >>>  phys_addr_t memblock_start_of_DRAM(void);
> >>>  phys_addr_t memblock_end_of_DRAM(void);
> >>>  void memblock_enforce_memory_limit(phys_addr_t memory_limit);
> >>>diff --git a/mm/memblock.c b/mm/memblock.c
> >>>index e81fb68f7f88..c1f1aac0459f 100644
> >>>--- a/mm/memblock.c
> >>>+++ b/mm/memblock.c
> >>>@@ -1729,6 +1729,25 @@ phys_addr_t __init_memblock memblock_reserved_size(void)
> >>>  	return memblock.reserved.total_size;
> >>>  }
> >>>+/**
> >>>+ * memblock_estimated_nr_pages - return number of pages from memblock point of
> >>>+ * view
> >>
> >>This function returns the estimate for free pages, not the number of pages
> >>in RAM.
> >>
> >>How about memblock_estimated_nr_free_pages()?
> >>
> >>>+ * some calculation before all pages are freed to buddy system, especially
> >>>+ * when CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
> >>
> >>I'm failing to parse this sentence. The return value here won't depend on
> >>CONFIG_DEFERRED_STRUCT_PAGE_INIT.
> >>
> >>>+ *
> >>>+ * At this point, we can get this information from memblock. Since the system
> >>>+ * state is not settle down and address alignment, the value is an estimation.
> >>>+ *
> >>>+ * Return:
> >>>+ * An estimated number of pages from memblock point of view.
> >>
> >>                            ^ free
> >>
> >>>+ */
> >>>+unsigned long __init memblock_estimated_nr_pages(void)
> >>>+{
> >>>+	return PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size());
> >>>+}
> >>>+
> >>>  /* lowest address */
> >>>  phys_addr_t __init_memblock memblock_start_of_DRAM(void)
> >>>  {
> >>>-- 
> >>>2.34.1
> >>>
> >
> >Thanks for review. Is this one looks better?
> >
> >Subject: [PATCH] mm/memblock: introduce a new helper memblock_estimated_nr_free_pages()
> >
> >During bootup, system may need the number of free pages in the whole system
> >to do some calculation before all pages are freed to buddy system. Usually
> >this number is get from totalram_pages(). Since we plan to move the free
> >pages accounting in __free_pages_core(), this value may not represent
> >total free pages at the early stage, especially when
> >CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
> >
> >Instead of using raw memblock api, let's introduce a new helper for user
> >to get the estimated number of free pages from memblock point of view.
> >
> >Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> >CC: David Hildenbrand <david@redhat.com>
> >---
> >  include/linux/memblock.h |  1 +
> >  mm/memblock.c            | 22 ++++++++++++++++++++++
> >  2 files changed, 23 insertions(+)
> >
> >diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> >index 40c62aca36ec..7d1c32b3dc12 100644
> >--- a/include/linux/memblock.h
> >+++ b/include/linux/memblock.h
> >@@ -486,6 +486,7 @@ static inline __init_memblock bool memblock_bottom_up(void)
> >  phys_addr_t memblock_phys_mem_size(void);
> >  phys_addr_t memblock_reserved_size(void);
> >+unsigned long memblock_estimated_nr_pages(void);
> >  phys_addr_t memblock_start_of_DRAM(void);
> >  phys_addr_t memblock_end_of_DRAM(void);
> >  void memblock_enforce_memory_limit(phys_addr_t memory_limit);
> >diff --git a/mm/memblock.c b/mm/memblock.c
> >index e81fb68f7f88..00decc42e02b 100644
> >--- a/mm/memblock.c
> >+++ b/mm/memblock.c
> >@@ -1729,6 +1729,28 @@ phys_addr_t __init_memblock memblock_reserved_size(void)
> >  	return memblock.reserved.total_size;
> >  }
> >+/**
> >+ * memblock_estimated_nr_free_pages - return estimated number of free pages
> >+ * from memblock point of view
> >+ *
> >+ * During bootup, system may need the number of free pages in the whole system
> >+ * to do some calculation before all pages are freed to buddy system. Usually
> >+ * this number is get from totalram_pages(). Since we plan to move the free
> >+ * pages accounting in __free_pages_core(), this value may not represent total
> >+ * free pages at the early stage, especially when > + * CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
> 
> These historical details should be dropped. "Since we plan ..." will easily
> get outdated soon.
> 
> * During bootup, subsystems might need a rough estimate of the number of *
> free pages in the whole system, before precise numbers are available
> * from the buddy. Especially with CONFIG_DEFERRED_STRUCT_PAGE_INIT, the
> * numbers obtained from the buddy might be very imprecise during bootup.
> 
> ?
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> -- 
> Cheers,
> 
> David / dhildenb
>