Re: [External] Re: [Linux-cachefs] [PATCH] cachefiles: make on-demand request distribution fairer

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On Wed, Aug 17, 2022 at 3:14 PM Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> wrote:
>
> Hi Yin,
>
> On Wed, Aug 17, 2022 at 02:52:00PM +0800, Xin Yin wrote:
> > For now, enqueuing and dequeuing on-demand requests all start from
> > idx 0, this makes request distribution unfair. In the weighty
> > concurrent I/O scenario, the request stored in higher idx will starve.
> >
> > Searching requests cyclically in cachefiles_ondemand_daemon_read,
> > makes distribution fairer.
>
> Yeah, thanks for the catch.  The previous approach could cause somewhat
> unfairness and make some requests starving... But we don't need strict
> FIFO here.
>
> >
> > Reported-by: Yongqing Li <liyongqing@xxxxxxxxxxxxx>
> > Signed-off-by: Xin Yin <yinxin.x@xxxxxxxxxxxxx>
> > ---
> >  fs/cachefiles/internal.h |  1 +
> >  fs/cachefiles/ondemand.c | 12 +++++++++---
> >  2 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
> > index 6cba2c6de2f9..2ad58c465208 100644
> > --- a/fs/cachefiles/internal.h
> > +++ b/fs/cachefiles/internal.h
> > @@ -111,6 +111,7 @@ struct cachefiles_cache {
> >       char                            *tag;           /* cache binding tag */
> >       refcount_t                      unbind_pincount;/* refcount to do daemon unbind */
> >       struct xarray                   reqs;           /* xarray of pending on-demand requests */
> > +     unsigned long                   req_id_next;
>
>         unsigned long                   ondemand_req_id_next; ?
Hi Xiang,

Thanks for the detailed review , whether "ondemand_req_id_next" is a
little long ? struct cachefiles_cache only holds on-demand requests ,
so I think "req_id_next" will not cause ambiguity. Does this make
sense?

Thanks,
Xin Yin
>
> Otherwise it looks good to me,
>
> Thanks,
> Gao Xiang
>
> >       struct xarray                   ondemand_ids;   /* xarray for ondemand_id allocation */
> >       u32                             ondemand_id_next;
> >  };
> > diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
> > index 1fee702d5529..247961d65369 100644
> > --- a/fs/cachefiles/ondemand.c
> > +++ b/fs/cachefiles/ondemand.c
> > @@ -238,14 +238,19 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
> >       unsigned long id = 0;
> >       size_t n;
> >       int ret = 0;
> > -     XA_STATE(xas, &cache->reqs, 0);
> > +     XA_STATE(xas, &cache->reqs, cache->req_id_next);
> >
> >       /*
> > -      * Search for a request that has not ever been processed, to prevent
> > -      * requests from being processed repeatedly.
> > +      * Cyclically search for a request that has not ever been processed,
> > +      * to prevent requests from being processed repeatedly, and make
> > +      * request distribution fair.
> >        */
> >       xa_lock(&cache->reqs);
> >       req = xas_find_marked(&xas, UINT_MAX, CACHEFILES_REQ_NEW);
> > +     if (!req && cache->req_id_next > 0) {
> > +             xas_set(&xas, 0);
> > +             req = xas_find_marked(&xas, cache->req_id_next - 1, CACHEFILES_REQ_NEW);
> > +     }
> >       if (!req) {
> >               xa_unlock(&cache->reqs);
> >               return 0;
> > @@ -260,6 +265,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
> >       }
> >
> >       xas_clear_mark(&xas, CACHEFILES_REQ_NEW);
> > +     cache->req_id_next = xas.xa_index + 1;
> >       xa_unlock(&cache->reqs);
> >
> >       id = xas.xa_index;
> > --
> > 2.25.1
> >
> > --
> > Linux-cachefs mailing list
> > Linux-cachefs@xxxxxxxxxx
> > https://listman.redhat.com/mailman/listinfo/linux-cachefs



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