From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, page_owner: record page owner for each subpage Patch series "debug_pagealloc improvements through page_owner", v2. The debug_pagealloc functionality serves a similar purpose on the page allocator level that slub_debug does on the kmalloc level, which is to detect bad users. One notable feature that slub_debug has is storing stack traces of who last allocated and freed the object. On page level we track allocations via page_owner, but that info is discarded when freeing, and we don't track freeing at all. This series improves those aspects. With both debug_pagealloc and page_owner enabled, we can then get bug reports such as the example in Patch 4. SLUB debug tracking additionally stores cpu, pid and timestamp. This could be added later, if deemed useful enough to justify the additional page_ext structure size. This patch (of 3): 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. Link: http://lkml.kernel.org/r/20190820131828.22684-3-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_owner.c | 40 ++++++++++++++++++++++++++++------------ 1 file changed, 28 insertions(+), 12 deletions(-) --- a/mm/page_owner.c~mm-page_owner-record-page-owner-for-each-subpage +++ a/mm/page_owner.c @@ -154,18 +154,23 @@ static noinline depot_stack_handle_t sav 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); + } } noinline void __set_page_owner(struct page *page, unsigned int order, @@ -178,7 +183,7 @@ noinline void __set_page_owner(struct pa return; handle = save_stack(gfp_mask); - __set_page_owner_handle(page_ext, handle, order, gfp_mask); + __set_page_owner_handle(page, page_ext, handle, order, gfp_mask); } void __set_page_owner_migrate_reason(struct page *page, int reason) @@ -204,8 +209,11 @@ void __split_page_owner(struct page *pag page_owner = get_page_owner(page_ext); page_owner->order = 0; - for (i = 1; i < (1 << order); i++) - __copy_page_owner(page, page + i); + for (i = 1; i < (1 << order); i++) { + page_ext = lookup_page_ext(page + i); + page_owner = get_page_owner(page_ext); + page_owner->order = 0; + } } void __copy_page_owner(struct page *oldpage, struct page *newpage) @@ -484,6 +492,13 @@ read_page_owner(struct file *file, char page_owner = get_page_owner(page_ext); /* + * Don't print "tail" pages of high-order allocations as that + * would inflate the stats. + */ + if (!IS_ALIGNED(pfn, 1 << page_owner->order)) + continue; + + /* * Access to page_ext->handle isn't synchronous so we should * be careful to access it. */ @@ -562,7 +577,8 @@ static void init_pages_in_zone(pg_data_t continue; /* Found early allocated page */ - __set_page_owner_handle(page_ext, early_handle, 0, 0); + __set_page_owner_handle(page, page_ext, early_handle, + 0, 0); count++; } cond_resched(); _
