Commit 1122f400 authored by Xin Yin's avatar Xin Yin Committed by David Howells
Browse files

cachefiles: make on-demand request distribution fairer 



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.

Fixes: c8383054 ("cachefiles: notify the user daemon when looking up cookie")
Reported-by: default avatarYongqing Li <liyongqing@bytedance.com>
Signed-off-by: default avatarXin Yin <yinxin.x@bytedance.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarJeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220817065200.11543-1-yinxin.x@bytedance.com/ # v1
Link: https://lore.kernel.org/r/20220825020945.2293-1-yinxin.x@bytedance.com/ # v2
parent c93ccd63

fs/cachefiles/internal.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

};

fs/cachefiles/ondemand.c

+9 −3
Original line number Diff line number Diff line
@@ -242,14 +242,19 @@ 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;
@@ -264,6 +269,7 @@ 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;