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    SubjectRe: [PATCH V2] lglock: add read-preference local-global rwlock
    On 03/05, Lai Jiangshan wrote:
    >
    > On 03/03/13 01:20, Oleg Nesterov wrote:
    > > On 03/02, Lai Jiangshan wrote:
    > >>
    > >> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
    > >> +{
    > >> + switch (__this_cpu_read(*lgrw->reader_refcnt)) {
    > >> + case 1:
    > >> + __this_cpu_write(*lgrw->reader_refcnt, 0);
    > >> + lg_local_unlock(&lgrw->lglock);
    > >> + return;
    > >> + case FALLBACK_BASE:
    > >> + __this_cpu_write(*lgrw->reader_refcnt, 0);
    > >> + read_unlock(&lgrw->fallback_rwlock);
    > >> + rwlock_release(&lg->lock_dep_map, 1, _RET_IP_);
    > >
    > > I guess "case 1:" should do rwlock_release() too.
    >
    > Already do it in "lg_local_unlock(&lgrw->lglock);" before it returns.
    > (I like reuse old code)

    Yes, I was wrong thanks. Another case when I didn't notice that you
    re-use the regular lg_ code...

    > > We need rwlock_acquire_read() even in the fast-path, and this acquire_read
    > > should be paired with rwlock_acquire() in _write_lock(), but it does
    > > spin_acquire(lg->lock_dep_map). Yes, currently this is the same (afaics)
    > > but perhaps fallback_rwlock->dep_map would be more clean.
    >
    > I can't tell which one is better. I try to use fallback_rwlock->dep_map later.

    I am not sure which one should be better too, please check.

    Again, I forgot that _write_lock/unlock use lg_global_*() code.

    Oleg.



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