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NFS: Improve heuristic for readdirplus

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The heuristic for readdirplus is designed to try to detect 'ls -l' and
similar patterns. It does so by looking for cache hit/miss patterns in
both the attribute cache and in the dcache of the files in a given
directory, and then sets a flag for the readdirplus code to interpret.

The problem with this approach is that a single attribute or dcache miss
can cause the NFS code to force a refresh of the attributes for the
entire set of files contained in the directory.

To be able to make a more nuanced decision, let's sample the number of
hits and misses in the set of open directory descriptors. That allows us
to set thresholds at which we start preferring READDIRPLUS over regular
READDIR, or at which we start to force a re-read of the remaining
readdir cache using READDIRPLUS.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Trond Myklebust
2022-02-17 11:08:24 -05:00
parent 9c3f4d988c
commit 230bc98f7a
5 changed files with 58 additions and 36 deletions
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5
include/linux/nfs_fs.h
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@@ -101,6 +101,8 @@ struct nfs_open_context {
struct nfs_open_dir_context {
struct list_head list;
atomic_t cache_hits;
atomic_t cache_misses;
unsigned long attr_gencount;
__be32 verf[NFS_DIR_VERIFIER_SIZE];
__u64 dir_cookie;
@@ -110,6 +112,7 @@ struct nfs_open_dir_context {
unsigned int dtsize;
signed char duped;
bool eof;
struct rcu_head rcu_head;
};
/*
@@ -274,13 +277,11 @@ struct nfs4_copy_state {
/*
* Bit offsets in flags field
*/
#define NFS_INO_ADVISE_RDPLUS (0) /* advise readdirplus */
#define NFS_INO_STALE (1) /* possible stale inode */
#define NFS_INO_ACL_LRU_SET (2) /* Inode is on the LRU list */
#define NFS_INO_INVALIDATING (3) /* inode is being invalidated */
#define NFS_INO_PRESERVE_UNLINKED (4) /* preserve file if removed while open */
#define NFS_INO_FSCACHE (5) /* inode can be cached by FS-Cache */
#define NFS_INO_FORCE_READDIR (7) /* force readdirplus */
#define NFS_INO_LAYOUTCOMMIT (9) /* layoutcommit required */
#define NFS_INO_LAYOUTCOMMITTING (10) /* layoutcommit inflight */
#define NFS_INO_LAYOUTSTATS (11) /* layoutstats inflight */