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XArray: add xa_get_order

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commit 57417cebc96b57122a2207fc84a6077d20c84b4b upstream

Patch series "Fix read-only THP for non-tmpfs filesystems".

As described more verbosely in the [3/3] changelog, we can inadvertently
put an order-0 page in the page cache which occupies 512 consecutive
entries.  Users are running into this if they enable the
READ_ONLY_THP_FOR_FS config option; see
https://bugzilla.kernel.org/show_bug.cgi?id=206569 and Qian Cai has also
reported it here:
https://lore.kernel.org/lkml/[email protected]/

This is a rather intrusive way of fixing the problem, but has the
advantage that I've actually been testing it with the THP patches, which
means that it sees far more use than it does upstream -- indeed, Song has
been entirely unable to reproduce it.  It also has the advantage that it
removes a few patches from my gargantuan backlog of THP patches.

This patch (of 3):

This function returns the order of the entry at the index.  We need this
because there isn't space in the shadow entry to encode its order.

[[email protected]: export xa_get_order to modules]

Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Song Liu <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Matthew Wilcox (Oracle) 2021-06-07 21:08:43 +01:00 • committed by Greg Kroah-Hartman
commit 03a390d879
3 changed files with 70 additions and 0 deletions
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21
lib/test_xarray.c
View file

@ -1649,6 +1649,26 @@ static noinline void check_account(struct xarray *xa)
#endif
}
static noinline void check_get_order(struct xarray *xa)
{
unsigned int max_order = IS_ENABLED(CONFIG_XARRAY_MULTI) ? 20 : 1;
unsigned int order;
unsigned long i, j;
for (i = 0; i < 3; i++)
XA_BUG_ON(xa, xa_get_order(xa, i) != 0);
for (order = 0; order < max_order; order++) {
for (i = 0; i < 10; i++) {
xa_store_order(xa, i << order, order,
xa_mk_index(i << order), GFP_KERNEL);
for (j = i << order; j < (i + 1) << order; j++)
XA_BUG_ON(xa, xa_get_order(xa, j) != order);
xa_erase(xa, i << order);
}
}
}
static noinline void check_destroy(struct xarray *xa)
{
unsigned long index;
@ -1697,6 +1717,7 @@ static int xarray_checks(void)
check_reserve(&array);
check_reserve(&xa0);
check_multi_store(&array);
check_get_order(&array);
check_xa_alloc();
check_find(&array);
check_find_entry(&array);

40
lib/xarray.c
View file

@ -1592,6 +1592,46 @@ unlock:
return xas_result(&xas, NULL);
}
EXPORT_SYMBOL(xa_store_range);
/**
* xa_get_order() - Get the order of an entry.
* @xa: XArray.
* @index: Index of the entry.
*
* Return: A number between 0 and 63 indicating the order of the entry.
*/
int xa_get_order(struct xarray *xa, unsigned long index)
{
XA_STATE(xas, xa, index);
void *entry;
int order = 0;
rcu_read_lock();
entry = xas_load(&xas);
if (!entry)
goto unlock;
if (!xas.xa_node)
goto unlock;
for (;;) {
unsigned int slot = xas.xa_offset + (1 << order);
if (slot >= XA_CHUNK_SIZE)
break;
if (!xa_is_sibling(xas.xa_node->slots[slot]))
break;
order++;
}
order += xas.xa_node->shift;
unlock:
rcu_read_unlock();
return order;
}
EXPORT_SYMBOL(xa_get_order);
#endif /* CONFIG_XARRAY_MULTI */
/**