[PATCH 5.19 045/155] cachefiles: make on-demand request distribution fairer

Greg Kroah-Hartman
2022-09-06T14:26:22Z

From: Xin Yin <yinxin.x@bytedance.com>

[ Upstream commit 1122f40072731525c06b1371cfa30112b9b54d27 ]

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: c8383054506c ("cachefiles: notify the user daemon when looking up cookie")
Reported-by: Yongqing Li <liyongqing@bytedance.com>
Signed-off-by: Xin Yin <yinxin.x@bytedance.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao 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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 6cba2c6de2f96..2ad58c4652084 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 7e1586bd5cf34..0254ed39f68ce 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -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;
--
2.35.1