Re: [PATCH v2] mm/compactoin: Fix misbehaviors of fast_find_migrateblock()

[Mel Gorman <mgorman@techsingularity.net>]

On Thu, Jan 28, 2021 at 03:01:27PM +0100, Vlastimil Babka wrote:
> On 1/28/21 2:50 PM, Wonhyuk Yang wrote:
> > On Thu, Jan 28, 2021 at 10:25 PM Mel Gorman <mgorman@techsingularity.net> wrote:
> >>
> >> As nr_scanned is post-incremented, this will still consider if the page
> >> should be used when the limit is reached. ++nr_scanned?
> > 
> > Hi,
> > 
> > Let's consider that limit is 4, nr_scanned is 0 and loop until reach the limit.
> > 1) pre-increment: it will search three times.(0,1,2)
> > 2) post-increment: it will search four times. (0,1,2,3)
> > 
> > So you mean that searching three times is correct?
> 
> 1) will match the outer loop's "nr_scanned < limit;" condition. It doesn't
> matter that much in practice, but for consistency sake, it should be 1)

Ok, while I find it a little strange to enter the loop and then break
immediately due to the limit, it's a marginal difference and in general,
the patch makes sense.

-- 
Mel Gorman
SUSE Labs