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

[Artem Bityutskiy]

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 (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ)
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