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

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Date:   Mon, 14 Nov 2022 10:53:25 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     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?

Other than that, from a tracing perspective:

  Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

for the series.

-- Steve


> +		__entry->failed = failed;
> +	),
> +
> +	TP_printk("va_start: %lu size=%lu align=%lu vstart=0x%lx vend=0x%lx failed=%d",
> +		__entry->addr, __entry->size, __entry->align,
> +		__entry->vstart, __entry->vend, __entry->failed)
> +);
> +
> +#endif /*  _TRACE_VMALLOC_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>