linux-kernel - Re: [PATCH v10 Golden] Unified trace buffer

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Date:	Mon, 29 Sep 2008 23:46:03 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v10 Golden] Unified trace buffer

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> On Mon, 29 Sep 2008, Mathieu Desnoyers wrote:
> > > 
> > > Thanks! I must have been lucky some how not to trigger this :-/
> > > 
> > 
> > My guess is that you never free your buffers in your test cases. I don't
> > know if it was expected; probably not if your code is built into the
> > kernel.
> 
> Actually my resize does free the buffers and I did test this. I probably 
> never ran the trace when testing the freeing which means those pointers 
> could have luckily not have been changed.
> 
> -- Steve
> 

I also got some corruption of the offset field in the struct page I use.
I think it might be related to the fact that I don't set the PG_private
bit (slob does set it when the page is in its free pages list). However,
given I'd like to pass the buffer pages to disk I/O and for network
socket and still keep the ability to re-use it when the I/O has been
performed, I wonder where I should put my 

                       struct list_head list;  /* linked list of buf pages */
                       size_t offset;          /* page offset in the buffer */

fields ? Any ideas ?

They are currently in :

struct buf_page {
        union {
                struct {
                        unsigned long flags;    /* mandatory */
                        atomic_t _count;        /* mandatory */
                        union {                 /* mandatory */
                                atomic_t _mapcount;
                                struct {
                                        u16 inuse;
                                        u16 objects;
                                };
                        };
                        struct list_head list;  /* linked list of buf pages */
                        size_t offset;          /* page offset in the buffer */
                };
                struct page page;
        };
};

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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