From 7e2f2a0cd17cfc42acb4b6a293d5cb6c7eda9862 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 23 Sep 2019 15:34:36 -0700 Subject: [PATCH] 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@suse.cz Signed-off-by: Vlastimil Babka Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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); + } } noinline void __set_page_owner(struct page *page, unsigned int order, @@ -178,7 +183,7 @@ noinline void __set_page_owner(struct page *page, unsigned int order, 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 *page, unsigned int order) 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) @@ -483,6 +491,13 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) 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 *pgdat, struct zone *zone) 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();