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    SubjectRe: [PATCH v4 05/11] writeback: create dirty_info structure
    On Fri, 29 Oct 2010 00:09:08 -0700
    Greg Thelen <gthelen@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.


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