Re: [PATCH V2 1/2] mm/damon/dbgfs: Modify Damon dbfs interface dependency in Kconfig

[Xin Hao]

Hi Park:

On 11/23/21 6:38 PM, SeongJae Park wrote:
> On Sun, 21 Nov 2021 22:07:04 +0800 Xin Hao <xhao@xxxxxxxxxxxxxxxxx> wrote:
>
> > If you want to support "DAMON_DBGFS" in config file, it only depends on
> > any one of "DAMON_VADDR" and "DAMON_PADDR", and sometimes we just want to
> > use damon virtual address function, but it is unreasonable to include "DAMON_PADDR"
> > in config file which cause the damon/paddr.c be compiled, so there fix it.
> Seems the above lines are not well wrapped[1].
>
> [1] https://docs.kernel.org/process/submitting-patches.html?highlight=75#the-canonical-patch-format
>
> > Signed-off-by: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/damon.h | 12 ++++++++++++
> >   mm/damon/Kconfig      |  2 +-
> >   2 files changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/damon.h b/include/linux/damon.h
> > index 8a73e825e0d5..00ad96f2ec10 100644
> > --- a/include/linux/damon.h
> > +++ b/include/linux/damon.h
> > @@ -463,11 +463,23 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
> >   #ifdef CONFIG_DAMON_VADDR
> >   void damon_va_set_primitives(struct damon_ctx *ctx);
> >   bool damon_va_target_valid(void *t);
> > +#else
> > +static inline void damon_va_set_primitives(struct damon_ctx *ctx) {}
> > +static inline bool damon_va_target_valid(void *t)
> > +{
> > +	return false;
> > +}
> >   #endif	/* CONFIG_DAMON_VADDR */
> >   
> >   #ifdef CONFIG_DAMON_PADDR
> >   void damon_pa_set_primitives(struct damon_ctx *ctx);
> >   bool damon_pa_target_valid(void *t);
> > +#else
> > +static inline void damon_pa_set_primitives(struct damon_ctx *ctx) {}
> > +static inline bool damon_pa_target_valid(void *t)
> > +{
> > +	return false;
> > +}
> >   #endif	/* CONFIG_DAMON_PADDR */
> >   
> >   #endif	/* _DAMON_H */
> > diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
> > index 5bcf05851ad0..971ffc496596 100644
> > --- a/mm/damon/Kconfig
> > +++ b/mm/damon/Kconfig
> > @@ -54,7 +54,7 @@ config DAMON_VADDR_KUNIT_TEST
> >   
> >   config DAMON_DBGFS
> >   	bool "DAMON debugfs interface"
> > -	depends on DAMON_VADDR && DAMON_PADDR && DEBUG_FS
> > +	depends on DAMON_VADDR || DAMON_PADDR && DEBUG_FS
> Due to the lack of parentheses, this allows enabling DAMON_DBGFS while DEBUG_FS
> is disabled.
>
> Sorry to say this but this makes me unsure if this patch is sufficiently
> tested.  I am also unsure if this patch is carefully handling all possible
> corner cases in appropriate ways.  For example, on kernels that doesn't having
> 'CONFIG_DAMON_PADDR=y', this patch would still make
> 'echo paddr > $debugfs/damon/target_ids' success.  Is that what you are
> intending?

Yes, you are all right, I have not tested as above, sorry, i did not 
fully consider the impact on the code after doing this,

Please ignore this patch.

> And, have you confirmed that will never make any issue, both in
> kernel space and the user space?  Could the behavioral change make the user
> space confused?
>
> Basically, reducing the dependency is a good idea.  But, IMHO, the benefit
> seems not so big.  After all, efficiency was not a first goal of DAMON debugfs
> interface.  That's why it is implemented on debugfs rather than its own
> specialized/optimized file system.  Better way for the efficiency of the user
> space interface might be inventing such DAMON's own efficient file system, like
> tracepoints had its interface on debugfs but now uses its own file system,
> tracefs.
>
> So, unless you make me believe the benefit is big enough and all possible
> corner cases are well handled and sufficiently tested, I'm sorry but I would
> not be convinced with this change.

I think it makes sense to separate PADDR & VADDR, users can freely 
choose dbfs + vaddr or dbfs + paddr;

Doing this can make the code look like it doesn’t mix together，i will 
continue to try to separate this part

of the code later.

> Thanks,
> SJ
>
> >   	help
> >   	  This builds the debugfs interface for DAMON.  The user space admins
> >   	  can use the interface for arbitrary data access monitoring.
> > --
> > 2.31.0

--
Best Regards!
Xin Hao