On Thu, Sep 12, 2024 at 11:56 AM Matthew Wilcox (Oracle)
<willy@xxxxxxxxxxxxx> wrote:
>
> Encode the type into the bottom four bits of page->private and the
> info into the remaining bits. Also turn the bootmem type into a
> named enum.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> arch/x86/mm/init_64.c | 9 ++++-----
> include/linux/bootmem_info.h | 25 +++++++++++++++++--------
> mm/bootmem_info.c | 11 ++++++-----
> mm/sparse.c | 8 ++++----
> 4 files changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..4d5fde324136 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -987,13 +987,12 @@ int arch_add_memory(int nid, u64 start, u64 size,
>
> static void __meminit free_pagetable(struct page *page, int order)
> {
> - unsigned long magic;
> - unsigned int nr_pages = 1 << order;
> -
> /* bootmem page has reserved flag */
> if (PageReserved(page)) {
> - magic = page->index;
> - if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
> + enum bootmem_type type = bootmem_type(page);
> + unsigned long nr_pages = 1 << order;
> +
> + if (type == SECTION_INFO || type == MIX_SECTION_INFO) {
> while (nr_pages--)
> put_page_bootmem(page++);
> } else
> diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
> index cffa38a73618..e2fe5de93dcc 100644
> --- a/include/linux/bootmem_info.h
> +++ b/include/linux/bootmem_info.h
> @@ -6,11 +6,10 @@
> #include <linux/kmemleak.h>
>
> /*
> - * Types for free bootmem stored in page->lru.next. These have to be in
> - * some random range in unsigned long space for debugging purposes.
> + * Types for free bootmem stored in the low bits of page->private.
> */
> -enum {
> - MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 12,
> +enum bootmem_type {
> + MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 1,
> SECTION_INFO = MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,
> MIX_SECTION_INFO,
> NODE_INFO,
> @@ -21,9 +20,19 @@ enum {
> void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
>
> void get_page_bootmem(unsigned long info, struct page *page,
> - unsigned long type);
> + enum bootmem_type type);
> void put_page_bootmem(struct page *page);
>
> +static inline enum bootmem_type bootmem_type(const struct page *page)
> +{
> + return (unsigned long)page->private & 0xf;
> +}
> +
> +static inline unsigned long bootmem_info(const struct page *page)
> +{
> + return (unsigned long)page->private >> 4;
> +}
Would it be better to define the number of bits used for the type as a
macro and use it throughout (bootmem_type(), bootmem_info(),
get_page_bootmem())?.
We can also add a static assertion or build bug in case 4 bits is not
enough anymore (e.g. if someone changes the enum values).
> +
> /*
> * Any memory allocated via the memblock allocator and not via the
> * buddy will be marked reserved already in the memmap. For those
> @@ -31,7 +40,7 @@ void put_page_bootmem(struct page *page);
> */
> static inline void free_bootmem_page(struct page *page)
> {
> - unsigned long magic = page->index;
> + enum bootmem_type type = bootmem_type(page);
>
> /*
> * The reserve_bootmem_region sets the reserved flag on bootmem
> @@ -39,7 +48,7 @@ static inline void free_bootmem_page(struct page *page)
> */
> VM_BUG_ON_PAGE(page_ref_count(page) != 2, page);
>
> - if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
> + if (type == SECTION_INFO || type == MIX_SECTION_INFO)
> put_page_bootmem(page);
> else
> VM_BUG_ON_PAGE(1, page);
> @@ -54,7 +63,7 @@ static inline void put_page_bootmem(struct page *page)
> }
>
> static inline void get_page_bootmem(unsigned long info, struct page *page,
> - unsigned long type)
> + enum bootmem_type type)
> {
> }
>
> diff --git a/mm/bootmem_info.c b/mm/bootmem_info.c
> index fa7cb0c87c03..95f288169a38 100644
> --- a/mm/bootmem_info.c
> +++ b/mm/bootmem_info.c
> @@ -14,23 +14,24 @@
> #include <linux/memory_hotplug.h>
> #include <linux/kmemleak.h>
>
> -void get_page_bootmem(unsigned long info, struct page *page, unsigned long type)
> +void get_page_bootmem(unsigned long info, struct page *page,
> + enum bootmem_type type)
> {
> - page->index = type;
> + BUG_ON(type > 0xf);
> + BUG_ON(info > (ULONG_MAX >> 4));
> SetPagePrivate(page);
> - set_page_private(page, info);
> + set_page_private(page, info << 4 | type);
> page_ref_inc(page);
> }
>
> void put_page_bootmem(struct page *page)
> {
> - unsigned long type = page->index;
> + enum bootmem_type type = bootmem_type(page);
>
> BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
> type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
>
> if (page_ref_dec_return(page) == 1) {
> - page->index = 0;
> ClearPagePrivate(page);
> set_page_private(page, 0);
> INIT_LIST_HEAD(&page->lru);
> diff --git a/mm/sparse.c b/mm/sparse.c
> index dc38539f8560..6ba5354cf2e1 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -720,19 +720,19 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
> static void free_map_bootmem(struct page *memmap)
> {
> unsigned long maps_section_nr, removing_section_nr, i;
> - unsigned long magic, nr_pages;
> + unsigned long type, nr_pages;
> struct page *page = virt_to_page(memmap);
>
> nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page))
> >> PAGE_SHIFT;
>
> for (i = 0; i < nr_pages; i++, page++) {
> - magic = page->index;
> + type = bootmem_type(page);
>
> - BUG_ON(magic == NODE_INFO);
> + BUG_ON(type == NODE_INFO);
>
> maps_section_nr = pfn_to_section_nr(page_to_pfn(page));
> - removing_section_nr = page_private(page);
> + removing_section_nr = bootmem_info(page);
>
> /*
> * When this function is called, the removing section is
> --
> 2.43.0
>
>
