On 8/17/22 2:52 PM, 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.
>
> 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;
> 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);
LGTM.
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> + }
> 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;
--
Thanks,
Jingbo
