linux-kernel - Re: [RFC PATCH 25/26] UBIFS: add debugging stuff

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Date:	Tue, 01 Apr 2008 09:20:58 +0300
From:	Artem Bityutskiy <dedekind@...dex.ru>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Adrian Hunter <ext-adrian.hunter@...ia.com>
Subject: Re: [RFC PATCH 25/26] UBIFS: add debugging stuff

Good day Pekka

>>  +void *dbg_vmalloc(size_t size)
>>  +
>>  +void dbg_vfree(void *addr)
>>  +
>>  +void dbg_leak_report(void)
>
> Not acceptable for mainline kernel. SLAB already provides leak
> detection and it should be straight-forward to port over to SLUB too.

Yeah, we will remove this later, keep it for now because it is very
convenient. I guess you refer the /proc/slab_allocations feature.
We found it less appropriate because it needs additional scripts to
be run to detect leaks, while this simple just hack makes UBIFS print
a message if there is a leak, which is just easier for us.

>>  +/*
>>  + * struct eaten_memory - memory object eaten by UBIFS to cause memory pressure.
>>  + * @list: link in the list of eaten memory objects
>>  + * @pad: just pads to memory page size
>>  + */
>>  +struct eaten_memory {
>>  +       struct list_head list;
>>  +       uint8_t pad[PAGE_CACHE_SIZE - sizeof(struct list_head)];
>>  +};
>
> If you need this, please make it a standalone module in mm/.

That was introduced to test the UBIFS shrinker, and to make sure
there are no races and everything works fine. Yes, will be removed
later.

>>  +#ifdef CONFIG_UBIFS_FS_DEBUG
>>  +#define UBIFS_DBG(op) op
>>  +#define ubifs_assert(expr)  do {                                               \
>>  +
>>  +/* Generic debugging message */
>>  +#define dbg_msg(fmt, ...) do {                                                 \
>>  +
>>  +/* Debugging message which prints UBIFS key */
>>  +#define dbg_key(c, key, fmt, ...) do {                                         \
>>  +
>>  +#define dbg_err(fmt, ...) ubifs_err(fmt, ##__VA_ARGS__)
>>  +#define dbg_dump_stack() dump_stack()
>
> Please kill these wrappers and use BUG_ON, WARN_ON, and printk() where
> appropriate.

Well, I do not see a big reason not to get rid of this harmless stuff.
Many kernel subsystems have their debugging, why not? Using BUG_ON() is
OK in few most important places. But we want to have more assertions
which are compiled-out by default, why can't we?. Similar is for prints.

Thanks for the feed-back. 

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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