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    SubjectRe: [RFC][PATCH] writeback: Unduplicate writeback reason
    Hi Steven,

    On Wed, Dec 14, 2011 at 09:14:00AM +0800, Steven Rostedt wrote:
    > Names of the writeback reasons are used in both the main kernel as well
    > as for parsing the tracepoint format file. Instead of duplicating the
    > names in two locations making it likely that they may become out of
    > sync, use some macro magic to make sure all the names stay in sync. Any
    > update only needs to happen in one spot for it to take place in all
    > locations.

    It looks a bit hacky, but does the nice job of de-duplicating code.
    And it compiles. So I like it and would like to take it with the below
    rename :-)

    > Note, this is an RFC patch, and it probably needs much better comments
    > (well, it currently has no comments), and the C() macro probably should
    > have a different name too.

    C => WB_ENUM_REASONS_ITEM? It may look unpleasantly long, however is
    unique enough to make the many #define/#undef safe.

    Thanks!
    Fengguang

    > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    >
    > Index: linux-trace.git/fs/fs-writeback.c
    > ===================================================================
    > --- linux-trace.git.orig/fs/fs-writeback.c
    > +++ linux-trace.git/fs/fs-writeback.c
    > @@ -47,15 +47,10 @@ struct wb_writeback_work {
    > struct completion *done; /* set if the caller waits */
    > };
    >
    > +#undef C
    > +#define C(a, b) [a] = b
    > const char *wb_reason_name[] = {
    > - [WB_REASON_BACKGROUND] = "background",
    > - [WB_REASON_TRY_TO_FREE_PAGES] = "try_to_free_pages",
    > - [WB_REASON_SYNC] = "sync",
    > - [WB_REASON_PERIODIC] = "periodic",
    > - [WB_REASON_LAPTOP_TIMER] = "laptop_timer",
    > - [WB_REASON_FREE_MORE_MEM] = "free_more_memory",
    > - [WB_REASON_FS_FREE_SPACE] = "fs_free_space",
    > - [WB_REASON_FORKER_THREAD] = "forker_thread"
    > + WB_ENUM_REASONS
    > };
    >
    > /*
    > Index: linux-trace.git/include/linux/writeback.h
    > ===================================================================
    > --- linux-trace.git.orig/include/linux/writeback.h
    > +++ linux-trace.git/include/linux/writeback.h
    > @@ -38,21 +38,23 @@ enum writeback_sync_modes {
    > WB_SYNC_ALL, /* Wait on every mapping */
    > };
    >
    > +#define WB_ENUM_REASONS \
    > + C(WB_REASON_BACKGROUND, "background"), \
    > + C(WB_REASON_TRY_TO_FREE_PAGES, "try_to_free_pages"), \
    > + C(WB_REASON_SYNC, "sync"), \
    > + C(WB_REASON_PERIODIC, "periodic"), \
    > + C(WB_REASON_LAPTOP_TIMER, "laptop_timer"), \
    > + C(WB_REASON_FREE_MORE_MEM, "free_more_memory"), \
    > + C(WB_REASON_FS_FREE_SPACE, "fs_free_space"), \
    > + C(WB_REASON_FORKER_THREAD, "forker_thread")
    > +
    > /*
    > * why some writeback work was initiated
    > */
    > -enum wb_reason {
    > - WB_REASON_BACKGROUND,
    > - WB_REASON_TRY_TO_FREE_PAGES,
    > - WB_REASON_SYNC,
    > - WB_REASON_PERIODIC,
    > - WB_REASON_LAPTOP_TIMER,
    > - WB_REASON_FREE_MORE_MEM,
    > - WB_REASON_FS_FREE_SPACE,
    > - WB_REASON_FORKER_THREAD,
    > +#undef C
    > +#define C(a, b) a
    > +enum wb_reason { WB_ENUM_REASONS, WB_REASONS_MAX };
    >
    > - WB_REASON_MAX,
    > -};
    > extern const char *wb_reason_name[];
    >
    > /*
    > Index: linux-trace.git/include/trace/events/writeback.h
    > ===================================================================
    > --- linux-trace.git.orig/include/trace/events/writeback.h
    > +++ linux-trace.git/include/trace/events/writeback.h
    > @@ -21,16 +21,11 @@
    > {I_REFERENCED, "I_REFERENCED"} \
    > )
    >
    > +#undef C
    > +#define C(a, b) {a, b}
    > #define show_work_reason(reason) \
    > __print_symbolic(reason, \
    > - {WB_REASON_BACKGROUND, "background"}, \
    > - {WB_REASON_TRY_TO_FREE_PAGES, "try_to_free_pages"}, \
    > - {WB_REASON_SYNC, "sync"}, \
    > - {WB_REASON_PERIODIC, "periodic"}, \
    > - {WB_REASON_LAPTOP_TIMER, "laptop_timer"}, \
    > - {WB_REASON_FREE_MORE_MEM, "free_more_memory"}, \
    > - {WB_REASON_FS_FREE_SPACE, "fs_free_space"}, \
    > - {WB_REASON_FORKER_THREAD, "forker_thread"} \
    > + WB_ENUM_REASONS \
    > )
    >
    > struct wb_writeback_work;
    >


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