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NFS: Use information about the change attribute to optimise updates

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If the NFSv4.2 server supports the 'change_attr_type' attribute, then
allow the client to optimise its attribute cache update strategy.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Trond Myklebust
2021-03-26 11:01:19 -04:00
parent 7f08a3359a
commit 6f9be83d07
2 changed files with 110 additions and 21 deletions
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111
fs/nfs/inode.c
View File

@ -1657,25 +1657,20 @@ EXPORT_SYMBOL_GPL(_nfs_display_fhandle);
#endif
/**
* nfs_inode_attrs_need_update - check if the inode attributes need updating
* @inode: pointer to inode
* nfs_inode_attrs_cmp_generic - compare attributes
* @fattr: attributes
* @inode: pointer to inode
*
* Attempt to divine whether or not an RPC call reply carrying stale
* attributes got scheduled after another call carrying updated ones.
*
* To do so, the function first assumes that a more recent ctime means
* that the attributes in fattr are newer, however it also attempt to
* catch the case where ctime either didn't change, or went backwards
* (if someone reset the clock on the server) by looking at whether
* or not this RPC call was started after the inode was last updated.
* Note also the check for wraparound of 'attr_gencount'
*
* The function returns 'true' if it thinks the attributes in 'fattr' are
* more recent than the ones cached in the inode.
*
* The function returns '1' if it thinks the attributes in @fattr are
* more recent than the ones cached in @inode. Otherwise it returns
* the value '0'.
*/
static int nfs_inode_attrs_need_update(const struct inode *inode, const struct nfs_fattr *fattr)
static int nfs_inode_attrs_cmp_generic(const struct nfs_fattr *fattr,
const struct inode *inode)
{
unsigned long attr_gencount = NFS_I(inode)->attr_gencount;
@ -1683,15 +1678,93 @@ static int nfs_inode_attrs_need_update(const struct inode *inode, const struct n
(long)(attr_gencount - nfs_read_attr_generation_counter()) > 0;
}
static int nfs_refresh_inode_locked(struct inode *inode, struct nfs_fattr *fattr)
/**
* nfs_inode_attrs_cmp_monotonic - compare attributes
* @fattr: attributes
* @inode: pointer to inode
*
* Attempt to divine whether or not an RPC call reply carrying stale
* attributes got scheduled after another call carrying updated ones.
*
* We assume that the server observes monotonic semantics for
* the change attribute, so a larger value means that the attributes in
* @fattr are more recent, in which case the function returns the
* value '1'.
* A return value of '0' indicates no measurable change
* A return value of '-1' means that the attributes in @inode are
* more recent.
*/
static int nfs_inode_attrs_cmp_monotonic(const struct nfs_fattr *fattr,
const struct inode *inode)
{
int ret;
s64 diff = fattr->change_attr - inode_peek_iversion_raw(inode);
if (diff > 0)
return 1;
return diff == 0 ? 0 : -1;
}
/**
* nfs_inode_attrs_cmp_strict_monotonic - compare attributes
* @fattr: attributes
* @inode: pointer to inode
*
* Attempt to divine whether or not an RPC call reply carrying stale
* attributes got scheduled after another call carrying updated ones.
*
* We assume that the server observes strictly monotonic semantics for
* the change attribute, so a larger value means that the attributes in
* @fattr are more recent, in which case the function returns the
* value '1'.
* A return value of '-1' means that the attributes in @inode are
* more recent or unchanged.
*/
static int nfs_inode_attrs_cmp_strict_monotonic(const struct nfs_fattr *fattr,
const struct inode *inode)
{
return nfs_inode_attrs_cmp_monotonic(fattr, inode) > 0 ? 1 : -1;
}
/**
* nfs_inode_attrs_cmp - compare attributes
* @fattr: attributes
* @inode: pointer to inode
*
* This function returns '1' if it thinks the attributes in @fattr are
* more recent than the ones cached in @inode. It returns '-1' if
* the attributes in @inode are more recent than the ones in @fattr,
* and it returns 0 if not sure.
*/
static int nfs_inode_attrs_cmp(const struct nfs_fattr *fattr,
const struct inode *inode)
{
if (nfs_inode_attrs_cmp_generic(fattr, inode) > 0)
return 1;
switch (NFS_SERVER(inode)->change_attr_type) {
case NFS4_CHANGE_TYPE_IS_UNDEFINED:
break;
case NFS4_CHANGE_TYPE_IS_TIME_METADATA:
if (!(fattr->valid & NFS_ATTR_FATTR_CHANGE))
break;
return nfs_inode_attrs_cmp_monotonic(fattr, inode);
default:
if (!(fattr->valid & NFS_ATTR_FATTR_CHANGE))
break;
return nfs_inode_attrs_cmp_strict_monotonic(fattr, inode);
}
return 0;
}
static int nfs_refresh_inode_locked(struct inode *inode,
struct nfs_fattr *fattr)
{
int attr_cmp = nfs_inode_attrs_cmp(fattr, inode);
int ret = 0;
trace_nfs_refresh_inode_enter(inode);
if (nfs_inode_attrs_need_update(inode, fattr))
if (attr_cmp > 0)
ret = nfs_update_inode(inode, fattr);
else
else if (attr_cmp == 0)
ret = nfs_check_inode_attributes(inode, fattr);
trace_nfs_refresh_inode_exit(inode, ret);
@ -1776,11 +1849,13 @@ EXPORT_SYMBOL_GPL(nfs_post_op_update_inode);
*/
int nfs_post_op_update_inode_force_wcc_locked(struct inode *inode, struct nfs_fattr *fattr)
{
int attr_cmp = nfs_inode_attrs_cmp(fattr, inode);
int status;
/* Don't do a WCC update if these attributes are already stale */
if ((fattr->valid & NFS_ATTR_FATTR) == 0 ||
!nfs_inode_attrs_need_update(inode, fattr)) {
if (attr_cmp < 0)
return 0;
if ((fattr->valid & NFS_ATTR_FATTR) == 0 || !attr_cmp) {
fattr->valid &= ~(NFS_ATTR_FATTR_PRECHANGE
| NFS_ATTR_FATTR_PRESIZE
| NFS_ATTR_FATTR_PREMTIME