linux-kernel - RE: [rfc] x86, ptrace: memory accounting for branch tracing

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Date:	Thu, 18 Dec 2008 15:57:53 +0000
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"roland@...hat.com" <roland@...hat.com>,
	"eranian@...glemail.com" <eranian@...glemail.com>
Subject: RE: [rfc] x86, ptrace: memory accounting for branch tracing

>-----Original Message-----
>From: Andrew Morton [mailto:akpm@...ux-foundation.org]
>Sent: Dienstag, 16. Dezember 2008 19:18
>To: Ingo Molnar
>Cc: Metzger, Markus T; Peter Zijlstra;

>> > Account memory allocated for the BTS buffer to the traced task's
>> > total_vm and locked_vm.
>>
>> Andrew, is this the right (and preferred) way to attach BTS buffer
>> allocation overhead to the RLIMIT_MEMLOCK bucket:
>
>Close.  I suspect we could refactor mlock.c to avoid all the code
>duplication we have there.
>
>There's (almost) nothing BTS-specific in this code, and it would be
>better if it lived in mm/mlock.c.  Hopefully in a
>usable-by-other-parts-of-mlock.c fashion.

Thanks,

I added alloc_locked_buffer() and free_locked_buffer() functions to mm/mlock.c.


>> > +static int ptrace_bts_allocate_buffer(struct task_struct
>*child, size_t size)
>> > +{
>> > +   unsigned long rlim, vm, pgsz;
>> > +   int error = -ENOMEM;
>> > +
>> > +   pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
>> > +
>> > +   down_write(&child->mm->mmap_sem);
>> > +
>> > +   rlim = child->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
>> > +   vm   = child->mm->total_vm + pgsz;
>> > +   if (rlim < vm)
>
>This is off-by-one, I think.  Should be
>
>        if (vm > rmlim)
>

Those two should be equivalent, shouldn't they?


regards,
markus.
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