nfsd: keep a checksum of the first 256 bytes of request
Now that we're allowing more DRC entries, it becomes a lot easier to hit
problems with XID collisions. In order to mitigate those, calculate a
checksum of up to the first 256 bytes of each request coming in and store
that in the cache entry, along with the total length of the request.
This initially used crc32, but Chuck Lever and Jim Rees pointed out that
crc32 is probably more heavyweight than we really need for generating
these checksums, and recommended looking at using the same routines that
are used to generate checksums for IP packets.
On an x86_64 KVM guest measurements with ftrace showed ~800ns to use
csum_partial vs ~1750ns for crc32. The difference probably isn't
terribly significant, but for now we may as well use csum_partial.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Stones-thrown-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
index 9c7232b..87fd141 100644
--- a/fs/nfsd/cache.h
+++ b/fs/nfsd/cache.h
@@ -29,6 +29,8 @@
u32 c_prot;
u32 c_proc;
u32 c_vers;
+ unsigned int c_len;
+ __wsum c_csum;
unsigned long c_timestamp;
union {
struct kvec u_vec;
@@ -73,6 +75,9 @@
/* Cache entries expire after this time period */
#define RC_EXPIRE (120 * HZ)
+/* Checksum this amount of the request */
+#define RC_CSUMLEN (256U)
+
int nfsd_reply_cache_init(void);
void nfsd_reply_cache_shutdown(void);
int nfsd_cache_lookup(struct svc_rqst *);