[Devel] Re: [PATCH v4 05/11] writeback: create dirty_info structure

[Greg Thelen]

Andrew Morton <akpm at linux-foundation.org> writes:

> On Fri, 29 Oct 2010 00:09:08 -0700
> Greg Thelen <gthelen at google.com> wrote:
>
>> Bundle dirty limits and dirty memory usage metrics into a dirty_info
>> structure to simplify interfaces of routines that need all.
>
> Problems...
>
> These patches interact pretty badly with Fengguang's "IO-less dirty
> throttling v2" patches.  I fixed up
> writeback-create-dirty_info-structure.patch pretty mechanically but
> when it got to memcg-check-memcg-dirty-limits-in-page-writeback.patch
> things got sticky and I gave up.
>
> As your stuff was merged first, I'd normally send the bad news to
> Fengguang, but the memcg code is logically built upon the core
> writeback code so I do think these patches should be staged after the
> changes to core writeback.
>
> Also, while I was there it seemed that the chosen members of the
> dirty_info structure were a bit random.  Perhaps we should be putting
> nr_dirty in there as well, perhaps other things.  Please have a think
> about that.
>
> Also, in ratelimit_pages() we call global_dirty_info() to return four
> items, but that caller only actually uses two of them.  Wasted effort?
>
>
> So I'm afraid I'm going to have to request that you redo and retest
> these patches:
>
> writeback-create-dirty_info-structure.patch
> memcg-add-dirty-page-accounting-infrastructure.patch
> memcg-add-kernel-calls-for-memcg-dirty-page-stats.patch
> memcg-add-dirty-limits-to-mem_cgroup.patch
> memcg-add-dirty-limits-to-mem_cgroup-use-native-word-to-represent-dirtyable-pages.patch
> memcg-add-dirty-limits-to-mem_cgroup-catch-negative-per-cpu-sums-in-dirty-info.patch
> memcg-add-dirty-limits-to-mem_cgroup-avoid-overflow-in-memcg_hierarchical_free_pages.patch
> memcg-add-dirty-limits-to-mem_cgroup-correct-memcg_hierarchical_free_pages-return-type.patch
> memcg-add-dirty-limits-to-mem_cgroup-avoid-free-overflow-in-memcg_hierarchical_free_pages.patch
> memcg-cpu-hotplug-lockdep-warning-fix.patch
> memcg-add-cgroupfs-interface-to-memcg-dirty-limits.patch
> memcg-break-out-event-counters-from-other-stats.patch
> memcg-check-memcg-dirty-limits-in-page-writeback.patch
> memcg-use-native-word-page-statistics-counters.patch
> memcg-use-native-word-page-statistics-counters-fix.patch
> #
> memcg-add-mem_cgroup-parameter-to-mem_cgroup_page_stat.patch
> memcg-pass-mem_cgroup-to-mem_cgroup_dirty_info.patch
> #memcg-make-throttle_vm_writeout-memcg-aware.patch: "troublesome": Kamezawa
> memcg-make-throttle_vm_writeout-memcg-aware.patch
> memcg-make-throttle_vm_writeout-memcg-aware-fix.patch
> memcg-simplify-mem_cgroup_page_stat.patch
> memcg-simplify-mem_cgroup_dirty_info.patch
> memcg-make-mem_cgroup_page_stat-return-value-unsigned.patch
>
> against the http://userweb.kernel.org/~akpm/mmotm/ which I just
> uploaded, sorry.  I've uploaded my copy of all the above to
> http://userweb.kernel.org/~akpm/stuff/gthelen.tar.gz.  I think only the
> two patches need fixing and retesting.
>
> Also, while wrangling the above patches, I stumbled across rejects such
> as:
>
>
> ***************
> *** 99,106 ****
>                    "state:            %8lx\n",
>                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
>                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
> -                  K(bdi_thresh), K(dirty_thresh),
> -                  K(background_thresh), nr_dirty, nr_io, nr_more_io,
>                    !list_empty(&bdi->bdi_list), bdi->state);
>   #undef K
>   
> --- 98,106 ----
>                    "state:            %8lx\n",
>                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
>                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
> +                  K(bdi_thresh), K(dirty_info.dirty_thresh),
> +                  K(dirty_info.background_thresh),
> +                  nr_dirty, nr_io, nr_more_io,
>                    !list_empty(&bdi->bdi_list), bdi->state);
>
> Please, if you discover crud like this, just fix it up.  One item per
> line:
>
>                    "state:            %8lx\n",
>                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
>                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
> 		   K(bdi_thresh),
> 		   K(dirty_info.dirty_thresh),
> 		   K(dirty_info.background_thresh),
> 		   nr_dirty,
> 		   nr_io,
> 		   nr_more_io,
>                    !list_empty(&bdi->bdi_list), bdi->state);
>
> all very simple.  And while you're there, fix up the
> tab-tab-space-space-space indenting - just use tabs.
>
>
> The other area where code maintenance is harder than it needs to be is
> in definitions of locals:
>
>         long nr_reclaimable;
>         long nr_dirty, bdi_dirty;  /* = file_dirty + writeback + unstable_nfs */
>         long bdi_prev_dirty = 0;
>
> again, that's just dopey.  Change it to
>
>         long nr_reclaimable;
>         long nr_dirty;
> 	long bdi_dirty;		/* = file_dirty + writeback + unstable_nfs */
>         long bdi_prev_dirty = 0;
>
> All very simple.
>
> Thanks.

I am leaving on vacation until Mon.  Once I return, this will be one of
the first things I get to.  I will resubmit patches based on whatever
the latest mmotm on Mon.
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