linux-kernel - Re: [PATCH v2 1/7] mm: vmalloc: Add alloc_vmap

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Date:   Mon, 14 Nov 2022 17:55:06 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v2 1/7] mm: vmalloc: Add alloc_vmap_area trace event

> On Tue, 18 Oct 2022 20:10:47 +0200
> "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:
> 
> > It is for a debug purpose and for validation of passed parameters.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > ---
> >  include/trace/events/vmalloc.h | 56 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 56 insertions(+)
> >  create mode 100644 include/trace/events/vmalloc.h
> > 
> > diff --git a/include/trace/events/vmalloc.h b/include/trace/events/vmalloc.h
> > new file mode 100644
> > index 000000000000..39fbd77c91e7
> > --- /dev/null
> > +++ b/include/trace/events/vmalloc.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM vmalloc
> > +
> > +#if !defined(_TRACE_VMALLOC_H) || defined(TRACE_HEADER_MULTI_READ)
> > +#define _TRACE_VMALLOC_H
> > +
> > +#include <linux/tracepoint.h>
> > +
> > +/**
> > + * alloc_vmap_area - called when a new vmap allocation occurs
> > + * @addr:	an allocated address
> > + * @size:	a requested size
> > + * @align:	a requested alignment
> > + * @vstart:	a requested start range
> > + * @vend:	a requested end range
> > + * @failed:	an allocation failed or not
> > + *
> > + * This event is used for a debug purpose, it can give an extra
> > + * information for a developer about how often it occurs and which
> > + * parameters are passed for further validation.
> > + */
> > +TRACE_EVENT(alloc_vmap_area,
> > +
> > +	TP_PROTO(unsigned long addr, unsigned long size, unsigned long align,
> > +		unsigned long vstart, unsigned long vend, int failed),
> > +
> > +	TP_ARGS(addr, size, align, vstart, vend, failed),
> 
> The above is passed in via (from patch 4):
> 
> 
> @@ -1621,6 +1624,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  		size, align, vstart, vend);
>  	spin_unlock(&free_vmap_area_lock);
>  
> +	trace_alloc_vmap_area(addr, size, align, vstart, vend, addr == vend);
> +
>  	/*
>  	 * If an allocation fails, the "vend" address is
>  	 * returned. Therefore trigger the overflow path.
> 
> > +
> > +	TP_STRUCT__entry(
> > +		__field(unsigned long, addr)
> > +		__field(unsigned long, size)
> > +		__field(unsigned long, align)
> > +		__field(unsigned long, vstart)
> > +		__field(unsigned long, vend)
> 
> > +		__field(int, failed)
> 
> I would drop the failed field...
> 
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->addr = addr;
> > +		__entry->size = size;
> > +		__entry->align = align;
> > +		__entry->vstart = vstart;
> > +		__entry->vend = vend;
> 
> And instead have:
> 
> 		__entry->failed = addr == vend;
> 
> Why pass in a parameter that can be calculated in the trace event logic?
>
It can be. A condition about when it is failed or not is taken on upper
level because it might be changed afterwards. So a trace event is not
aware about it thus no need in adaptation.

But i do not have a strong opinion here. I can prepare a patch to
eliminate it.

What is your preference?

--
Uladzislau Rezki