| Message ID | 20240821173914.2270383-4-willy@infradead.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Increase the number of bits available in page_type | expand |
On 21.08.24 19:39, Matthew Wilcox (Oracle) wrote: > By using a few values in the top byte, users of page_type can store up > to 24 bits of additional data in page_type. It also reduces the code > size as (with replacement of READ_ONCE() with data_race()), the kernel > can check just a single byte. eg: > > ffffffff811e3a79: 8b 47 30 mov 0x30(%rdi),%eax > ffffffff811e3a7c: 55 push %rbp > ffffffff811e3a7d: 48 89 e5 mov %rsp,%rbp > ffffffff811e3a80: 25 00 00 00 82 and $0x82000000,%eax > ffffffff811e3a85: 3d 00 00 00 80 cmp $0x80000000,%eax > ffffffff811e3a8a: 74 4d je ffffffff811e3ad9 <folio_mapping+0x69> > > becomes: > > ffffffff811e3a69: 80 7f 33 f5 cmpb $0xf5,0x33(%rdi) > ffffffff811e3a6d: 55 push %rbp > ffffffff811e3a6e: 48 89 e5 mov %rsp,%rbp > ffffffff811e3a71: 74 4d je ffffffff811e3ac0 <folio_mapping+0x60> > > replacing three instructions with one. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Acked-by: David Hildenbrand <david@redhat.com>
Hi Matthew, On 2024/8/22 1:39, Matthew Wilcox (Oracle) wrote: > By using a few values in the top byte, users of page_type can store up > to 24 bits of additional data in page_type. It also reduces the code > size as (with replacement of READ_ONCE() with data_race()), the kernel > can check just a single byte. eg: > > ffffffff811e3a79: 8b 47 30 mov 0x30(%rdi),%eax > ffffffff811e3a7c: 55 push %rbp > ffffffff811e3a7d: 48 89 e5 mov %rsp,%rbp > ffffffff811e3a80: 25 00 00 00 82 and $0x82000000,%eax > ffffffff811e3a85: 3d 00 00 00 80 cmp $0x80000000,%eax > ffffffff811e3a8a: 74 4d je ffffffff811e3ad9 <folio_mapping+0x69> > > becomes: > > ffffffff811e3a69: 80 7f 33 f5 cmpb $0xf5,0x33(%rdi) > ffffffff811e3a6d: 55 push %rbp > ffffffff811e3a6e: 48 89 e5 mov %rsp,%rbp > ffffffff811e3a71: 74 4d je ffffffff811e3ac0 <folio_mapping+0x60> > > replacing three instructions with one. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > include/linux/page-flags.h | 68 ++++++++++++++++---------------------- > kernel/vmcore_info.c | 8 ++--- > mm/debug.c | 31 +++++++++++++---- > 3 files changed, 56 insertions(+), 51 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 998a99441e4f..0c738bda5d98 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -923,42 +923,29 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) > #endif > > /* > - * For pages that are never mapped to userspace, > - * page_type may be used. Because it is initialised to -1, we invert the > - * sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and > - * __ClearPageFoo *sets* the bit used for PageFoo. We reserve a few high and > - * low bits so that an underflow or overflow of _mapcount won't be > - * mistaken for a page type value. > + * For pages that do not use mapcount, page_type may be used. > + * The low 24 bits of pagetype may be used for your own purposes, as long > + * as you are careful to not affect the top 8 bits. The low bits of > + * pagetype will be overwritten when you clear the page_type from the page. > */ > - > enum pagetype { > - PG_buddy = 0x40000000, > - PG_offline = 0x20000000, > - PG_table = 0x10000000, > - PG_guard = 0x08000000, > - PG_hugetlb = 0x04000000, > - PG_slab = 0x02000000, > - PG_zsmalloc = 0x01000000, > - PG_unaccepted = 0x00800000, > - > - PAGE_TYPE_BASE = 0x80000000, > - > - /* > - * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and > - * allow owners that set a type to reuse the lower 16 bit for their own > - * purposes. > - */ > - PAGE_MAPCOUNT_RESERVE = ~0x0000ffff, > + /* 0x00-0x7f are positive numbers, ie mapcount */ > + /* Reserve 0x80-0xef for mapcount overflow. */ > + PGTY_buddy = 0xf0, > + PGTY_offline = 0xf1, > + PGTY_table = 0xf2, > + PGTY_guard = 0xf3, > + PGTY_hugetlb = 0xf4, > + PGTY_slab = 0xf5, > + PGTY_zsmalloc = 0xf6, > + PGTY_unaccepted = 0xf7, > + > + PGTY_mapcount_underflow = 0xff > }; > > -#define PageType(page, flag) \ > - ((READ_ONCE(page->page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > -#define folio_test_type(folio, flag) \ > - ((READ_ONCE(folio->page.page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > - > static inline bool page_type_has_type(int page_type) > { > - return page_type < PAGE_MAPCOUNT_RESERVE; > + return page_type < (PGTY_mapcount_underflow << 24); > } > > /* This takes a mapcount which is one more than page->_mapcount */ > @@ -969,40 +956,41 @@ static inline bool page_mapcount_is_type(unsigned int mapcount) > > static inline bool page_has_type(const struct page *page) > { > - return page_type_has_type(READ_ONCE(page->page_type)); > + return page_mapcount_is_type(data_race(page->page_type)); > } > > #define FOLIO_TYPE_OPS(lname, fname) \ > -static __always_inline bool folio_test_##fname(const struct folio *folio)\ > +static __always_inline bool folio_test_##fname(const struct folio *folio) \ > { \ > - return folio_test_type(folio, PG_##lname); \ > + return data_race(folio->page.page_type >> 24) == PGTY_##lname; \ > } \ > static __always_inline void __folio_set_##fname(struct folio *folio) \ > { \ > - VM_BUG_ON_FOLIO(!folio_test_type(folio, 0), folio); \ > - folio->page.page_type &= ~PG_##lname; \ > + VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX, \ > + folio); \ > + folio->page.page_type = PGTY_##lname << 24; \ > } \ > static __always_inline void __folio_clear_##fname(struct folio *folio) \ > { \ > VM_BUG_ON_FOLIO(!folio_test_##fname(folio), folio); \ > - folio->page.page_type |= PG_##lname; \ > + folio->page.page_type = UINT_MAX; \ > } > > #define PAGE_TYPE_OPS(uname, lname, fname) \ > FOLIO_TYPE_OPS(lname, fname) \ > static __always_inline int Page##uname(const struct page *page) \ > { \ > - return PageType(page, PG_##lname); \ > + return data_race(page->page_type >> 24) == PGTY_##lname; \ > } \ > static __always_inline void __SetPage##uname(struct page *page) \ > { \ > - VM_BUG_ON_PAGE(!PageType(page, 0), page); \ > - page->page_type &= ~PG_##lname; \ > + VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page); \ > + page->page_type = PGTY_##lname << 24; \ > } \ > static __always_inline void __ClearPage##uname(struct page *page) \ > { \ > VM_BUG_ON_PAGE(!Page##uname(page), page); \ > - page->page_type |= PG_##lname; \ > + page->page_type = UINT_MAX; \ > } > There are some UBSAN warning about __folio_set_##fname/__SetPage##uname, UBSAN: shift-out-of-bounds in ../include/linux/page-flags.h:998:1 left shift of 240 by 24 places cannot be represented in type 'int' ... Changing significant bit to unsigned to fix it. diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 28d2337525d1..2175ebceb41c 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -966,7 +966,7 @@ static __always_inline void __folio_set_##fname(struct folio *folio) \ { \ VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX, \ folio); \ - folio->page.page_type = PGTY_##lname << 24; \ + folio->page.page_type = (unsigned int)PGTY_##lname << 24; \ } \ static __always_inline void __folio_clear_##fname(struct folio *folio) \ { \ @@ -983,7 +983,7 @@ static __always_inline int Page##uname(const struct page *page) \ static __always_inline void __SetPage##uname(struct page *page) \ { \ VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page); \ - page->page_type = PGTY_##lname << 24; \ + page->page_type = (unsigned int)PGTY_##lname << 24; \ } \
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 998a99441e4f..0c738bda5d98 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -923,42 +923,29 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) #endif /* - * For pages that are never mapped to userspace, - * page_type may be used. Because it is initialised to -1, we invert the - * sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and - * __ClearPageFoo *sets* the bit used for PageFoo. We reserve a few high and - * low bits so that an underflow or overflow of _mapcount won't be - * mistaken for a page type value. + * For pages that do not use mapcount, page_type may be used. + * The low 24 bits of pagetype may be used for your own purposes, as long + * as you are careful to not affect the top 8 bits. The low bits of + * pagetype will be overwritten when you clear the page_type from the page. */ - enum pagetype { - PG_buddy = 0x40000000, - PG_offline = 0x20000000, - PG_table = 0x10000000, - PG_guard = 0x08000000, - PG_hugetlb = 0x04000000, - PG_slab = 0x02000000, - PG_zsmalloc = 0x01000000, - PG_unaccepted = 0x00800000, - - PAGE_TYPE_BASE = 0x80000000, - - /* - * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and - * allow owners that set a type to reuse the lower 16 bit for their own - * purposes. - */ - PAGE_MAPCOUNT_RESERVE = ~0x0000ffff, + /* 0x00-0x7f are positive numbers, ie mapcount */ + /* Reserve 0x80-0xef for mapcount overflow. */ + PGTY_buddy = 0xf0, + PGTY_offline = 0xf1, + PGTY_table = 0xf2, + PGTY_guard = 0xf3, + PGTY_hugetlb = 0xf4, + PGTY_slab = 0xf5, + PGTY_zsmalloc = 0xf6, + PGTY_unaccepted = 0xf7, + + PGTY_mapcount_underflow = 0xff }; -#define PageType(page, flag) \ - ((READ_ONCE(page->page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) -#define folio_test_type(folio, flag) \ - ((READ_ONCE(folio->page.page_type) & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) - static inline bool page_type_has_type(int page_type) { - return page_type < PAGE_MAPCOUNT_RESERVE; + return page_type < (PGTY_mapcount_underflow << 24); } /* This takes a mapcount which is one more than page->_mapcount */ @@ -969,40 +956,41 @@ static inline bool page_mapcount_is_type(unsigned int mapcount) static inline bool page_has_type(const struct page *page) { - return page_type_has_type(READ_ONCE(page->page_type)); + return page_mapcount_is_type(data_race(page->page_type)); } #define FOLIO_TYPE_OPS(lname, fname) \ -static __always_inline bool folio_test_##fname(const struct folio *folio)\ +static __always_inline bool folio_test_##fname(const struct folio *folio) \ { \ - return folio_test_type(folio, PG_##lname); \ + return data_race(folio->page.page_type >> 24) == PGTY_##lname; \ } \ static __always_inline void __folio_set_##fname(struct folio *folio) \ { \ - VM_BUG_ON_FOLIO(!folio_test_type(folio, 0), folio); \ - folio->page.page_type &= ~PG_##lname; \ + VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX, \ + folio); \ + folio->page.page_type = PGTY_##lname << 24; \ } \ static __always_inline void __folio_clear_##fname(struct folio *folio) \ { \ VM_BUG_ON_FOLIO(!folio_test_##fname(folio), folio); \ - folio->page.page_type |= PG_##lname; \ + folio->page.page_type = UINT_MAX; \ } #define PAGE_TYPE_OPS(uname, lname, fname) \ FOLIO_TYPE_OPS(lname, fname) \ static __always_inline int Page##uname(const struct page *page) \ { \ - return PageType(page, PG_##lname); \ + return data_race(page->page_type >> 24) == PGTY_##lname; \ } \ static __always_inline void __SetPage##uname(struct page *page) \ { \ - VM_BUG_ON_PAGE(!PageType(page, 0), page); \ - page->page_type &= ~PG_##lname; \ + VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page); \ + page->page_type = PGTY_##lname << 24; \ } \ static __always_inline void __ClearPage##uname(struct page *page) \ { \ VM_BUG_ON_PAGE(!Page##uname(page), page); \ - page->page_type |= PG_##lname; \ + page->page_type = UINT_MAX; \ } /* diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c index 8b4f8cc2e0ec..1fec61603ef3 100644 --- a/kernel/vmcore_info.c +++ b/kernel/vmcore_info.c @@ -198,17 +198,17 @@ static int __init crash_save_vmcoreinfo_init(void) VMCOREINFO_NUMBER(PG_private); VMCOREINFO_NUMBER(PG_swapcache); VMCOREINFO_NUMBER(PG_swapbacked); -#define PAGE_SLAB_MAPCOUNT_VALUE (~PG_slab) +#define PAGE_SLAB_MAPCOUNT_VALUE (PGTY_slab << 24) VMCOREINFO_NUMBER(PAGE_SLAB_MAPCOUNT_VALUE); #ifdef CONFIG_MEMORY_FAILURE VMCOREINFO_NUMBER(PG_hwpoison); #endif VMCOREINFO_NUMBER(PG_head_mask); -#define PAGE_BUDDY_MAPCOUNT_VALUE (~PG_buddy) +#define PAGE_BUDDY_MAPCOUNT_VALUE (PGTY_buddy << 24) VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE); -#define PAGE_HUGETLB_MAPCOUNT_VALUE (~PG_hugetlb) +#define PAGE_HUGETLB_MAPCOUNT_VALUE (PGTY_hugetlb << 24) VMCOREINFO_NUMBER(PAGE_HUGETLB_MAPCOUNT_VALUE); -#define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline) +#define PAGE_OFFLINE_MAPCOUNT_VALUE (PGTY_offline << 24) VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE); #ifdef CONFIG_KALLSYMS diff --git a/mm/debug.c b/mm/debug.c index 9f8e34537957..aa57d3ffd4ed 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -36,11 +36,6 @@ const struct trace_print_flags pageflag_names[] = { {0, NULL} }; -const struct trace_print_flags pagetype_names[] = { - __def_pagetype_names, - {0, NULL} -}; - const struct trace_print_flags gfpflag_names[] = { __def_gfpflag_names, {0, NULL} @@ -51,6 +46,27 @@ const struct trace_print_flags vmaflag_names[] = { {0, NULL} }; +#define DEF_PAGETYPE_NAME(_name) [PGTY_##_name - 0xf0] = __stringify(_name) + +static const char *page_type_names[] = { + DEF_PAGETYPE_NAME(slab), + DEF_PAGETYPE_NAME(hugetlb), + DEF_PAGETYPE_NAME(offline), + DEF_PAGETYPE_NAME(guard), + DEF_PAGETYPE_NAME(table), + DEF_PAGETYPE_NAME(buddy), + DEF_PAGETYPE_NAME(unaccepted), +}; + +static const char *page_type_name(unsigned int page_type) +{ + unsigned i = (page_type >> 24) - 0xf0; + + if (i >= ARRAY_SIZE(page_type_names)) + return "unknown"; + return page_type_names[i]; +} + static void __dump_folio(struct folio *folio, struct page *page, unsigned long pfn, unsigned long idx) { @@ -58,7 +74,7 @@ static void __dump_folio(struct folio *folio, struct page *page, int mapcount = atomic_read(&page->_mapcount); char *type = ""; - mapcount = page_type_has_type(mapcount) ? 0 : mapcount + 1; + mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount + 1; pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n", folio_ref_count(folio), mapcount, mapping, folio->index + idx, pfn); @@ -92,7 +108,8 @@ static void __dump_folio(struct folio *folio, struct page *page, pr_warn("%sflags: %pGp%s\n", type, &folio->flags, is_migrate_cma_folio(folio, pfn) ? " CMA" : ""); if (page_has_type(&folio->page)) - pr_warn("page_type: %x\n", folio->page.page_type); + pr_warn("page_type: %x(%s)\n", folio->page.page_type >> 24, + page_type_name(folio->page.page_type)); print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32, sizeof(unsigned long), page,
By using a few values in the top byte, users of page_type can store up to 24 bits of additional data in page_type. It also reduces the code size as (with replacement of READ_ONCE() with data_race()), the kernel can check just a single byte. eg: ffffffff811e3a79: 8b 47 30 mov 0x30(%rdi),%eax ffffffff811e3a7c: 55 push %rbp ffffffff811e3a7d: 48 89 e5 mov %rsp,%rbp ffffffff811e3a80: 25 00 00 00 82 and $0x82000000,%eax ffffffff811e3a85: 3d 00 00 00 80 cmp $0x80000000,%eax ffffffff811e3a8a: 74 4d je ffffffff811e3ad9 <folio_mapping+0x69> becomes: ffffffff811e3a69: 80 7f 33 f5 cmpb $0xf5,0x33(%rdi) ffffffff811e3a6d: 55 push %rbp ffffffff811e3a6e: 48 89 e5 mov %rsp,%rbp ffffffff811e3a71: 74 4d je ffffffff811e3ac0 <folio_mapping+0x60> replacing three instructions with one. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- include/linux/page-flags.h | 68 ++++++++++++++++---------------------- kernel/vmcore_info.c | 8 ++--- mm/debug.c | 31 +++++++++++++---- 3 files changed, 56 insertions(+), 51 deletions(-)