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Message-Id: <20090622122755.21F6.A69D9226@jp.fujitsu.com>
Date: Mon, 22 Jun 2009 12:37:10 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Rik van Riel <riel@...hat.com>
Cc: kosaki.motohiro@...fujitsu.com,
Larry Woodman <lwoodman@...hat.com>,
Ingo Molnar <mingo@...e.hu>,
Fr馘駻ic Weisbecker
<fweisbec@...il.com>, Li Zefan <lizf@...fujitsu.com>,
Pekka Enberg <penberg@...helsinki.fi>,
eduard.munteanu@...ux360.ro, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, rostedt@...dmis.org
Subject: Re: [Patch] mm tracepoints update - use case.
> Larry Woodman wrote:
>
> >> - Please don't display mm and/or another kernel raw pointer.
> >> if we assume non stop system, we can't use kernel-dump. Thus kernel pointer
> >> logging is not so useful.
> >
> > OK, I just dont know how valuable the trace output is with out some raw
> > data like the mm_struct.
>
> I believe that we do want something like the mm_struct in
> the trace info, so we can figure out which process was
> allocating pages, etc...
Yes.
I think we need to print tgid, it is needed to imporove CONFIG_MM_OWNER.
current CONFIG_MM_OWNER back-pointer point to semi-random task_struct.
> >> - Please consider how do this feature works on mem-cgroup.
> >> (IOW, please don't ignore many "if (scanning_global_lru())")
>
> Good point, we want to trace cgroup vs non-cgroup reclaims,
> too.
thank you.
>
> >> - tracepoint caller shouldn't have any assumption of displaying representation.
> >> e.g.
> >> wrong) trace_mm_pagereclaim_pgout(mapping, page->index<<PAGE_SHIFT, PageAnon(page));
> >> good) trace_mm_pagereclaim_pgout(mapping, page)
> >
> > OK.
> >
> >> that's general and good callback and/or hook manner.
>
> How do we figure those out from the page pointer at the time
> the tracepoint triggers?
>
> I believe that it would be useful to export that info in the
> trace point, since we cannot expect the userspace trace tool
> to figure out these things from the struct page address.
>
> Or did I overlook something here?
current, TRACE_EVENT have two step information trasformation.
- step1 - TP_fast_assign()
it is called from tracepoint directly. it makes ring-buffer representaion.
- step2 - TP_printk
it is called when reading debug/tracing/trace file. it makes printable
representation from ring-buffer data.
example:
trace_sched_switch() has three argument, rq, prev, next.
--------------------------------------------------
static inline void
context_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next)
{
(snip)
trace_sched_switch(rq, prev, next);
-------------------------------------------------
TP_fast_assing extract data from argument pointer.
-----------------------------------------------------
TP_fast_assign(
memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
__entry->prev_pid = prev->pid;
__entry->prev_prio = prev->prio;
__entry->prev_state = prev->state;
memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
__entry->next_pid = next->pid;
__entry->next_prio = next->prio;
),
-----------------------------------------------------
I think mm tracepoint can do the same way.
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