Mike Kravetz <mike.kravetz@xxxxxxxxxx> writes:
On 06/05/23 17:26, Ackerley Tng wrote:
Mike Kravetz <mike.kravetz@xxxxxxxxxx> writes:
This doesn't seem to work as expected:
Here's a test I did
...
The above gave me: page_cache_next_miss(xa, 4, 3): 7
But I was expecting a return value of 6.
I investigated a little, and it seems like entry at index 6 if we start
iterating before 6 is 0xe, and xa_is_internal(entry) returns true.
Not yet familiar with the internals of xarrays, not sure what the fix
should be.
I am NOT an expert with xarray. However, the documentation says:
"Calling xa_store_range() stores the same entry in a range
of indices. If you do this, some of the other operations will behave
in a slightly odd way. For example, marking the entry at one index
may result in the entry being marked at some, but not all of the other
indices. Storing into one index may result in the entry retrieved by
some, but not all of the other indices changing."
This may be why your test is not functioning as expected? I modified
your check_find_5() routine as follows (within lib/test_xarray.c):
static noinline void check_find_5(struct xarray *xa, bool mult)
{
unsigned long max_scan;
void *p = &max_scan;
XA_BUG_ON(xa, !xa_empty(xa));
if (mult) {
xa_store(xa, 3, p, GFP_KERNEL);
xa_store(xa, 4, p, GFP_KERNEL);
xa_store(xa, 5, p, GFP_KERNEL);
} else {
xa_store_range(xa, 3, 5, p, GFP_KERNEL);
}
max_scan = 3;
if (mult)
printk("---> multiple stores\n");
else
printk("---> range store\n");
printk("page_cache_next_miss(xa, %d, %ld): %ld\n", 4, max_scan,
__page_cache_next_miss(xa, 4, max_scan));
if (mult) {
xa_store(xa, 3, NULL, GFP_KERNEL);
xa_store(xa, 4, NULL, GFP_KERNEL);
xa_store(xa, 5, NULL, GFP_KERNEL);
} else {
xa_store_range(xa, 3, 5, NULL, GFP_KERNEL);
}
xa_destroy(xa);
}
This results in:
[ 149.998676] ---> multiple stores
[ 149.999391] page_cache_next_miss(xa, 4, 3): 6
[ 150.003342] ---> range store
[ 150.007002] page_cache_next_miss(xa, 4, 3): 7
I am fairly confident the page cache code will make individual xa_store
calls as opposed to xa_store_range.
I tried this out with xa_store and a non-NULL pointer, and it works as
expected. Thanks!
I also checked that filemap/page_cache doesn't use xa_store_range(). It
only uses xas_store().
Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Tested-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
