Re: balance_pgdat(): where is total_scanned ever updated?

[Andrew Morton <akpm@osdl.org>]

Chuck Ebbert <76306.1226@compuserve.com> wrote:
>
> Kernel version is 2.6.9, but I see no updates to this function in BK-current.
> How is total_scanned ever updated?  AFAICT it is always zero.

It's a bug which was introduced months ago when we added struct
reclaim_state.

> In mm/vmscan.c:balance_pgdat(), there are these references to total_scanned
> (missing whitepace indicated by "^"):
> 
> 
>  977:        int total_scanned, total_reclaimed;
> 
>  983:        total_scanned = 0;
> 
> 1076:                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
> 1077:                            total_scanned > total_reclaimed+total_reclaimed/2)
>                                                                ^ ^             ^ ^
> 
> 1088:                if (total_scanned && priority < DEF_PRIORITY - 2)
> 
> 
> Could this be part of the problems with reclaim?  Or have I missed something?

I had a patch which fixes it in -mm for a while.  It does increase the
number of pages which are reclaimed via direct reclaim and decreases the
number of pages which are reclaimed by kswapd.  As one would expect from
throttling kswapd.  This seems undesirable.

I'm leaving this alone until it can be demonstrated that fixing it improves
kernel behaviour in some manner.