On 9/24/19 1:31 PM, Kirill A. Shutemov wrote: > On Tue, Aug 20, 2019 at 03:18:26PM +0200, Vlastimil Babka wrote: >> Currently, page owner info is only recorded for the first page of a >> high-order >> allocation, and copied to tail pages in the event of a split page. With the >> plan to keep previous owner info after freeing the page, it would be >> benefical >> to record page owner for each subpage upon allocation. This increases the >> overhead for high orders, but that should be acceptable for a debugging >> option. >> >> The order stored for each subpage is the order of the whole allocation. This >> makes it possible to calculate the "head" pfn and to recognize "tail" pages >> (quoted because not all high-order allocations are compound pages with true >> head and tail pages). When reading the page_owner debugfs file, keep skipping >> the "tail" pages so that stats gathered by existing scripts don't get >> inflated. >> >> Signed-off-by: Vlastimil Babka <[email protected]> >> --- >> mm/page_owner.c | 40 ++++++++++++++++++++++++++++------------ >> 1 file changed, 28 insertions(+), 12 deletions(-) >> >> diff --git a/mm/page_owner.c b/mm/page_owner.c >> index addcbb2ae4e4..813fcb70547b 100644 >> --- a/mm/page_owner.c >> +++ b/mm/page_owner.c >> @@ -154,18 +154,23 @@ static noinline depot_stack_handle_t save_stack(gfp_t >> flags) >> return handle; >> } >> >> -static inline void __set_page_owner_handle(struct page_ext *page_ext, >> - depot_stack_handle_t handle, unsigned int order, gfp_t gfp_mask) >> +static inline void __set_page_owner_handle(struct page *page, >> + struct page_ext *page_ext, depot_stack_handle_t handle, >> + unsigned int order, gfp_t gfp_mask) >> { >> struct page_owner *page_owner; >> + int i; >> >> - page_owner = get_page_owner(page_ext); >> - page_owner->handle = handle; >> - page_owner->order = order; >> - page_owner->gfp_mask = gfp_mask; >> - page_owner->last_migrate_reason = -1; >> + for (i = 0; i < (1 << order); i++) { >> + page_owner = get_page_owner(page_ext); >> + page_owner->handle = handle; >> + page_owner->order = order; >> + page_owner->gfp_mask = gfp_mask; >> + page_owner->last_migrate_reason = -1; >> + __set_bit(PAGE_EXT_OWNER, &page_ext->flags); >> >> - __set_bit(PAGE_EXT_OWNER, &page_ext->flags); >> + page_ext = lookup_page_ext(page + i); > > Isn't it off-by-one? You are calculating page_ext for the next page, > right?
You're right, thanks! > And cant we just do page_ext++ here instead? Unfortunately no, as that implies sizeof(page_ext), which only declares unsigned long flags; and the rest is runtime-determined. Perhaps I could add a wrapper named e.g. page_ext_next() that would use get_entry_size() internally and hide the necessary casts to void * and back?
