[PATCH v13 62/72] dax: Hash on XArray instead of mapping

From: Matthew Wilcox
Date: Mon Jun 11 2018 - 10:13:02 EST


From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>

Since the XArray is embedded in the struct address_space, its address
contains exactly as much entropy as the address of the mapping. This
patch is purely preparatory for later patches which will simplify the
wait/wake interfaces.

Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
---
fs/dax.c | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 97e8931541f1..7d0712c45da5 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -116,7 +116,7 @@ static int dax_is_empty_entry(void *entry)
* DAX page cache entry locking
*/
struct exceptional_entry_key {
- struct address_space *mapping;
+ struct xarray *xa;
pgoff_t entry_start;
};

@@ -125,7 +125,7 @@ struct wait_exceptional_entry_queue {
struct exceptional_entry_key key;
};

-static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
+static wait_queue_head_t *dax_entry_waitqueue(struct xarray *xa,
pgoff_t index, void *entry, struct exceptional_entry_key *key)
{
unsigned long hash;
@@ -138,21 +138,21 @@ static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
if (dax_is_pmd_entry(entry))
index &= ~PG_PMD_COLOUR;

- key->mapping = mapping;
+ key->xa = xa;
key->entry_start = index;

- hash = hash_long((unsigned long)mapping ^ index, DAX_WAIT_TABLE_BITS);
+ hash = hash_long((unsigned long)xa ^ index, DAX_WAIT_TABLE_BITS);
return wait_table + hash;
}

-static int wake_exceptional_entry_func(wait_queue_entry_t *wait, unsigned int mode,
- int sync, void *keyp)
+static int wake_exceptional_entry_func(wait_queue_entry_t *wait,
+ unsigned int mode, int sync, void *keyp)
{
struct exceptional_entry_key *key = keyp;
struct wait_exceptional_entry_queue *ewait =
container_of(wait, struct wait_exceptional_entry_queue, wait);

- if (key->mapping != ewait->key.mapping ||
+ if (key->xa != ewait->key.xa ||
key->entry_start != ewait->key.entry_start)
return 0;
return autoremove_wake_function(wait, mode, sync, NULL);
@@ -163,13 +163,13 @@ static int wake_exceptional_entry_func(wait_queue_entry_t *wait, unsigned int mo
* The important information it's conveying is whether the entry at
* this index used to be a PMD entry.
*/
-static void dax_wake_mapping_entry_waiter(struct address_space *mapping,
+static void dax_wake_mapping_entry_waiter(struct xarray *xa,
pgoff_t index, void *entry, bool wake_all)
{
struct exceptional_entry_key key;
wait_queue_head_t *wq;

- wq = dax_entry_waitqueue(mapping, index, entry, &key);
+ wq = dax_entry_waitqueue(xa, index, entry, &key);

/*
* Checking for locked entry and prepare_to_wait_exclusive() happens
@@ -246,7 +246,8 @@ static void *get_unlocked_mapping_entry(struct address_space *mapping,
return entry;
}

- wq = dax_entry_waitqueue(mapping, index, entry, &ewait.key);
+ wq = dax_entry_waitqueue(&mapping->i_pages, index, entry,
+ &ewait.key);
prepare_to_wait_exclusive(wq, &ewait.wait,
TASK_UNINTERRUPTIBLE);
xa_unlock_irq(&mapping->i_pages);
@@ -270,7 +271,7 @@ static void dax_unlock_mapping_entry(struct address_space *mapping,
}
unlock_slot(mapping, slot);
xa_unlock_irq(&mapping->i_pages);
- dax_wake_mapping_entry_waiter(mapping, index, entry, false);
+ dax_wake_mapping_entry_waiter(&mapping->i_pages, index, entry, false);
}

static void put_locked_mapping_entry(struct address_space *mapping,
@@ -290,7 +291,7 @@ static void put_unlocked_mapping_entry(struct address_space *mapping,
return;

/* We have to wake up next waiter for the page cache entry lock */
- dax_wake_mapping_entry_waiter(mapping, index, entry, false);
+ dax_wake_mapping_entry_waiter(&mapping->i_pages, index, entry, false);
}

static unsigned long dax_entry_size(void *entry)
@@ -481,8 +482,8 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
dax_disassociate_entry(entry, mapping, false);
radix_tree_delete(&mapping->i_pages, index);
mapping->nrexceptional--;
- dax_wake_mapping_entry_waiter(mapping, index, entry,
- true);
+ dax_wake_mapping_entry_waiter(&mapping->i_pages,
+ index, entry, true);
}

entry = dax_make_locked(0, size_flag | DAX_EMPTY);
--
2.17.1