1

netfs: Prep to use folio->private for write grouping and streaming write

Prepare to use folio->private to hold information write grouping and
streaming write.  These are implemented in the same commit as they both
make use of folio->private and will be both checked at the same time in
several places.

"Write grouping" involves ordering the writeback of groups of writes, such
as is needed for ceph snaps.  A group is represented by a
filesystem-supplied object which must contain a netfs_group struct.  This
contains just a refcount and a pointer to a destructor.

"Streaming write" is the storage of data in folios that are marked dirty,
but not uptodate, to avoid unnecessary reads of data.  This is represented
by a netfs_folio struct.  This contains the offset and length of the
modified region plus the otherwise displaced write grouping pointer.

The way folio->private is multiplexed is:

 (1) If private is NULL then neither is in operation on a dirty folio.

 (2) If private is set, with bit 0 clear, then this points to a group.

 (3) If private is set, with bit 0 set, then this points to a netfs_folio
     struct (with bit 0 AND'ed out).

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
This commit is contained in:
David Howells 2023-09-29 17:28:25 +01:00
parent 4fcccc38eb
commit 9ebff83e64
3 changed files with 115 additions and 0 deletions

View File

@ -149,6 +149,34 @@ static inline bool netfs_is_cache_enabled(struct netfs_inode *ctx)
#endif #endif
} }
/*
* Get a ref on a netfs group attached to a dirty page (e.g. a ceph snap).
*/
static inline struct netfs_group *netfs_get_group(struct netfs_group *netfs_group)
{
if (netfs_group)
refcount_inc(&netfs_group->ref);
return netfs_group;
}
/*
* Dispose of a netfs group attached to a dirty page (e.g. a ceph snap).
*/
static inline void netfs_put_group(struct netfs_group *netfs_group)
{
if (netfs_group && refcount_dec_and_test(&netfs_group->ref))
netfs_group->free(netfs_group);
}
/*
* Dispose of a netfs group attached to a dirty page (e.g. a ceph snap).
*/
static inline void netfs_put_group_many(struct netfs_group *netfs_group, int nr)
{
if (netfs_group && refcount_sub_and_test(nr, &netfs_group->ref))
netfs_group->free(netfs_group);
}
/* /*
* fscache-cache.c * fscache-cache.c
*/ */

View File

@ -177,9 +177,55 @@ EXPORT_SYMBOL(netfs_clear_inode_writeback);
*/ */
void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length) void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
{ {
struct netfs_folio *finfo = NULL;
size_t flen = folio_size(folio);
_enter("{%lx},%zx,%zx", folio_index(folio), offset, length); _enter("{%lx},%zx,%zx", folio_index(folio), offset, length);
folio_wait_fscache(folio); folio_wait_fscache(folio);
if (!folio_test_private(folio))
return;
finfo = netfs_folio_info(folio);
if (offset == 0 && length >= flen)
goto erase_completely;
if (finfo) {
/* We have a partially uptodate page from a streaming write. */
unsigned int fstart = finfo->dirty_offset;
unsigned int fend = fstart + finfo->dirty_len;
unsigned int end = offset + length;
if (offset >= fend)
return;
if (end <= fstart)
return;
if (offset <= fstart && end >= fend)
goto erase_completely;
if (offset <= fstart && end > fstart)
goto reduce_len;
if (offset > fstart && end >= fend)
goto move_start;
/* A partial write was split. The caller has already zeroed
* it, so just absorb the hole.
*/
}
return;
erase_completely:
netfs_put_group(netfs_folio_group(folio));
folio_detach_private(folio);
folio_clear_uptodate(folio);
kfree(finfo);
return;
reduce_len:
finfo->dirty_len = offset + length - finfo->dirty_offset;
return;
move_start:
finfo->dirty_len -= offset - finfo->dirty_offset;
finfo->dirty_offset = offset;
} }
EXPORT_SYMBOL(netfs_invalidate_folio); EXPORT_SYMBOL(netfs_invalidate_folio);

View File

@ -140,6 +140,47 @@ struct netfs_inode {
#define NETFS_ICTX_ODIRECT 0 /* The file has DIO in progress */ #define NETFS_ICTX_ODIRECT 0 /* The file has DIO in progress */
}; };
/*
* A netfs group - for instance a ceph snap. This is marked on dirty pages and
* pages marked with a group must be flushed before they can be written under
* the domain of another group.
*/
struct netfs_group {
refcount_t ref;
void (*free)(struct netfs_group *netfs_group);
};
/*
* Information about a dirty page (attached only if necessary).
* folio->private
*/
struct netfs_folio {
struct netfs_group *netfs_group; /* Filesystem's grouping marker (or NULL). */
unsigned int dirty_offset; /* Write-streaming dirty data offset */
unsigned int dirty_len; /* Write-streaming dirty data length */
};
#define NETFS_FOLIO_INFO 0x1UL /* OR'd with folio->private. */
static inline struct netfs_folio *netfs_folio_info(struct folio *folio)
{
void *priv = folio_get_private(folio);
if ((unsigned long)priv & NETFS_FOLIO_INFO)
return (struct netfs_folio *)((unsigned long)priv & ~NETFS_FOLIO_INFO);
return NULL;
}
static inline struct netfs_group *netfs_folio_group(struct folio *folio)
{
struct netfs_folio *finfo;
void *priv = folio_get_private(folio);
finfo = netfs_folio_info(folio);
if (finfo)
return finfo->netfs_group;
return priv;
}
/* /*
* Resources required to do operations on a cache. * Resources required to do operations on a cache.
*/ */