On 10/9/22 04:25, Zhaoyang Huang wrote: > On Fri, Oct 7, 2022 at 6:08 PM Vlastimil Babka <vbabka@xxxxxxx> wrote: >> >> On 10/6/22 05:19, zhaoyang.huang wrote: >> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> >> > >> > Private is vacant for most of Non-LRU pages while the user has explicitly >> > operation on page->private via set_page_private, I would like introduce >> > stackdepot information on page->private for a simplified tracking mechanism >> > which could be help for kernel driver's memory leak. >> > >> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> >> >> This duplicates the existing page_owner functionality in a way that >> unconditionally adds overhead to all kernels that have CONFIG_STACKDEPOT >> enabled build-time (and also misses the need to initialize stackdepot properly). > Sure. This patch could be deemed as a light and complement of the page > owner which depends on proc fs in lived system for showing the result. > This patch could be mainly helpful on RAM dump as it is hard to find > page_ext for page owners. I also would like to make this optional via > defconfig item. I'm still not convinced we need this, between existing page_owner and the proposed code tagging framework. https://lore.kernel.org/all/20220830214919.53220-1-surenb@xxxxxxxxxx/ For finding page_ext in crash dumps, it's possible with a scriptable debugger like drgn or crash-python. >> >> Also wouldn't be suprised if some existing page->private users were actually >> confused by the field suddenly being non-zero without their own action. > IMO, the existing page->private users will cover this field directly > without distrubed by handle. Well the bot wasn't happy so far https://lore.kernel.org/all/202210072204.cfea59d3-oliver.sang@xxxxxxxxx/ >> >> > --- >> > mm/page_alloc.c | 28 +++++++++++++++++++++++++++- >> > 1 file changed, 27 insertions(+), 1 deletion(-) >> > >> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> > index e5486d4..b79a503 100644 >> > --- a/mm/page_alloc.c >> > +++ b/mm/page_alloc.c >> > @@ -75,6 +75,7 @@ >> > #include <linux/khugepaged.h> >> > #include <linux/buffer_head.h> >> > #include <linux/delayacct.h> >> > +#include <linux/stackdepot.h> >> > #include <asm/sections.h> >> > #include <asm/tlbflush.h> >> > #include <asm/div64.h> >> > @@ -2464,6 +2465,25 @@ static inline bool should_skip_init(gfp_t flags) >> > return (flags & __GFP_SKIP_ZERO); >> > } >> > >> > +#ifdef CONFIG_STACKDEPOT >> > +static noinline depot_stack_handle_t set_track_prepare(void) >> > +{ >> > + depot_stack_handle_t trace_handle; >> > + unsigned long entries[16]; >> > + unsigned int nr_entries; >> > + >> > + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3); >> > + trace_handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT); >> > + >> > + return trace_handle; >> > +} >> > +#else >> > +static inline depot_stack_handle_t set_track_prepare(void) >> > +{ >> > + return 0; >> > +} >> > +#endif >> > + >> > inline void post_alloc_hook(struct page *page, unsigned int order, >> > gfp_t gfp_flags) >> > { >> > @@ -2471,8 +2491,14 @@ inline void post_alloc_hook(struct page *page, unsigned int order, >> > !should_skip_init(gfp_flags); >> > bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS); >> > int i; >> > + depot_stack_handle_t stack_handle = set_track_prepare(); >> > >> > - set_page_private(page, 0); >> > + /* >> > + * Don't worry, user will cover private directly without checking >> > + * this field and has ability to trace the page. This also will not >> > + * affect expected state when freeing >> > + */ >> > + set_page_private(page, stack_handle); >> > set_page_refcounted(page); >> > >> > arch_alloc_page(page, order); >>
