Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> It's perfectly legal to have compound pages in the page cache. Call
> find_subpage(page, xas.xa_index) unconditionally.
Like this?
#define iterate_mapping(i, n, __v, skip, STEP) { \
struct page *page; \
size_t wanted = n, seg, offset; \
loff_t start = i->mapping_start + skip; \
pgoff_t index = start >> PAGE_SHIFT; \
\
XA_STATE(xas, &i->mapping->i_pages, index); \
\
rcu_read_lock(); \
xas_for_each(&xas, page, ULONG_MAX) { \
if (xas_retry(&xas, page) || xa_is_value(page)) { \
WARN_ON(1); \
break; \
} \
__v.bv_page = find_subpage(page, xas.xa_index); \
offset = (i->mapping_start + skip) & ~PAGE_MASK; \
seg = PAGE_SIZE - offset; \
__v.bv_offset = offset; \
__v.bv_len = min(n, seg); \
(void)(STEP); \
n -= __v.bv_len; \
skip += __v.bv_len; \
if (n == 0) \
break; \
} \
rcu_read_unlock(); \
n = wanted - n; \
}
Note that the walk is not restartable - and the array is supposed to have been
fully populated by the caller for the range specified - so I've made it print
a warning and end the loop if xas_retry() or xa_is_value() return true (which
takes care of the !page case too). Possibly I could just leave it to fault in
this case and not check.
If PageHuge(page) is true, I presume I need to support that too. How do I
find out how big the page is?
David
