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Thu, 9 Mar 2023 17:31:14 -0500 (EST) References: <20230210214645.2720847-1-shr@devkernel.io> <20230309172726.14fca32e@gandalf.local.home> User-agent: mu4e 1.6.11; emacs 28.2.50 From: Stefan Roesch To: Steven Rostedt Cc: kernel-team@fb.com, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH v1] mm: add tracepoints to ksm Date: Thu, 09 Mar 2023 14:30:34 -0800 In-reply-to: <20230309172726.14fca32e@gandalf.local.home> Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Steven Rostedt writes: > On Fri, 10 Feb 2023 13:46:45 -0800 > Stefan Roesch wrote: > > Sorry for the late reply, I just noticed this (I had the flu when this was > originally sent). > >> +/** >> + * ksm_remove_ksm_page - called after a ksm page has been removed >> + * >> + * @pfn: page frame number of ksm page >> + * >> + * Allows to trace the removing of stable ksm pages. >> + */ >> +TRACE_EVENT(ksm_remove_ksm_page, >> + >> + TP_PROTO(unsigned long pfn), >> + >> + TP_ARGS(pfn), >> + >> + TP_STRUCT__entry( >> + __field(unsigned long, pfn) >> + ), >> + >> + TP_fast_assign( >> + __entry->pfn = pfn; >> + ), >> + >> + TP_printk("pfn %lu", __entry->pfn) >> +); >> + >> +/** >> + * ksm_remove_rmap_item - called after a rmap_item has been removed from the >> + * stable tree >> + * >> + * @pfn: page frame number of ksm page >> + * @rmap_item: address of rmap_item object >> + * @mm: address of the process mm struct >> + * >> + * Allows to trace the removal of pages from the stable tree list. >> + */ >> +TRACE_EVENT(ksm_remove_rmap_item, >> + >> + TP_PROTO(unsigned long pfn, void *rmap_item, void *mm), >> + >> + TP_ARGS(pfn, rmap_item, mm), >> + >> + TP_STRUCT__entry( >> + __field(unsigned long, pfn) >> + __field(void *, rmap_item) >> + __field(void *, mm) >> + ), >> + >> + TP_fast_assign( >> + __entry->pfn = pfn; >> + __entry->rmap_item = rmap_item; >> + __entry->mm = mm; >> + ), >> + >> + TP_printk("pfn %lu rmap_item %p mm %p", >> + __entry->pfn, __entry->rmap_item, __entry->mm) >> +); >> + >> +#endif /* _TRACE_KSM_H */ >> + >> +/* This part must be outside protection */ >> +#include >> diff --git a/mm/ksm.c b/mm/ksm.c >> index 56808e3bfd19..4356af760735 100644 >> --- a/mm/ksm.c >> +++ b/mm/ksm.c >> @@ -45,6 +45,9 @@ >> #include "internal.h" >> #include "mm_slot.h" >> >> +#define CREATE_TRACE_POINTS >> +#include >> + >> #ifdef CONFIG_NUMA >> #define NUMA(x) (x) >> #define DO_NUMA(x) do { (x); } while (0) >> @@ -655,10 +658,12 @@ static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node) >> BUG_ON(stable_node->rmap_hlist_len < 0); >> >> hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { >> - if (rmap_item->hlist.next) >> + if (rmap_item->hlist.next) { >> ksm_pages_sharing--; >> - else >> + trace_ksm_remove_rmap_item(stable_node->kpfn, rmap_item, rmap_item->mm); > > Instead of dereferencing the stable_node here, where the work could > possibly happen outside the trace event and in the hot path, could you pass > in the stable_node instead, and then in the TP_fast_assign() do: > > __entry->pfn = stable_node->kpfn; > > I'll make the change in the next version. >> + } else { >> ksm_pages_shared--; >> + } >> >> rmap_item->mm->ksm_merging_pages--; >> >> @@ -679,6 +684,7 @@ static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node) >> BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); >> BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); >> >> + trace_ksm_remove_ksm_page(stable_node->kpfn); > > Here too? > > -- Steve > I'll make the change in the next version. >> if (stable_node->head == &migrate_nodes) >> list_del(&stable_node->list); >> else >> @@ -1367,6 +1373,8 @@ static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item, >> get_anon_vma(vma->anon_vma); >> out: >> mmap_read_unlock(mm); >> + trace_ksm_merge_with_ksm_page(kpage, page_to_pfn(kpage ? kpage : page), >> + rmap_item, mm, err); >> return err; >> } >> >> @@ -2114,6 +2122,9 @@ static int try_to_merge_with_kernel_zero_page(struct ksm_rmap_item *rmap_item, >> if (vma) { >> err = try_to_merge_one_page(vma, page, >> ZERO_PAGE(rmap_item->address)); >> + trace_ksm_merge_one_page( >> + page_to_pfn(ZERO_PAGE(rmap_item->address)), >> + rmap_item, mm, err); >> if (!err) { >> rmap_item->address |= ZERO_PAGE_FLAG; >> ksm_zero_pages_sharing++; >> @@ -2344,6 +2355,8 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) >> >> mm_slot = ksm_scan.mm_slot; >> if (mm_slot == &ksm_mm_head) { >> + trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items); >> + >> /* >> * A number of pages can hang around indefinitely on per-cpu >> * pagevecs, raised page count preventing write_protect_page >> @@ -2510,6 +2523,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) >> if (mm_slot != &ksm_mm_head) >> goto next_mm; >> >> + trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items); >> ksm_scan.seqnr++; >> return NULL; >> } >> @@ -2661,6 +2675,7 @@ int __ksm_enter(struct mm_struct *mm) >> if (needs_wakeup) >> wake_up_interruptible(&ksm_thread_wait); >> >> + trace_ksm_enter(mm); >> return 0; >> } >> >> @@ -2702,6 +2717,8 @@ void __ksm_exit(struct mm_struct *mm) >> mmap_write_lock(mm); >> mmap_write_unlock(mm); >> } >> + >> + trace_ksm_exit(mm); >> } >> >> struct page *ksm_might_need_to_copy(struct page *page, >> >> base-commit: 234a68e24b120b98875a8b6e17a9dead277be16a