Re: [PATCH V2 2/2] mm: compaction: Limit the value of interface compact_memory

[Luis Chamberlain <mcgrof@kernel.org>]

On Wed, Mar 08, 2023 at 11:23:45AM +0100, Vlastimil Babka wrote:
> 
> 
> On 3/6/23 07:05, ye.xingchen@zte.com.cn wrote:
> > From: Minghao Chi <chi.minghao@zte.com.cn>
> > 
> > Available only when CONFIG_COMPACTION is set. When 1 is written to
> > the file, all zones are compacted such that free memory is available
> > in contiguous blocks where possible.
> > But echo others-parameter > compact_memory, this function will be
> > triggered by writing parameters to the interface.
> > 
> > Applied this patch,
> > sh/$ echo 1.1 > /proc/sys/vm/compact_memory
> > sh/$ sh: write error: Invalid argument
> > The start and end time of printing triggering compact_memory.
> > 
> > Link: https://lore.kernel.org/all/ZAJwoXJCzfk1WIBx@bombadil.infradead.org/
> > Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
> > Signed-off-by: Ye Xingchen <ye.xingchen@zte.com.cn>
> > ---
> >  mm/compaction.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 5a9501e0ae01..2c9ecc4b9d23 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -2763,6 +2763,8 @@ int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
> >  	return 0;
> >  }
> > 
> > +/* The written value is actually unused, all memory is compacted */
> > +int sysctl_compact_memory;
> >  /*
> >   * This is the entry point for compacting all nodes via
> >   * /proc/sys/vm/compact_memory
> > @@ -2770,8 +2772,16 @@ int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
> >  int sysctl_compaction_handler(struct ctl_table *table, int write,
> >  			void *buffer, size_t *length, loff_t *ppos)
> >  {
> > -	if (write)
> > +	int ret;
> > +
> > +	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
> > +	if (ret)
> > +		return ret;
> > +	if (write) {
> > +		pr_info("compact_nodes start\n");
> >  		compact_nodes();
> > +		pr_info("compact_nodes end\n");
> 
> I'm not sure we want to start spamming the dmesg. This would make sense
> if we wanted to deprecate the sysctl and start hunting for remaining
> callers to be fixed. Otherwise ftrace can be used to capture e.g. the time.

Without that print, I don't think a custom proc handler is needed too,
right? So what would simplify the code.

  Luis