BLKS_PER_BUF
#define BUFFER_SIZE (BLKS_PER_BUF*PAGE_SIZE)
struct page *pages[BLKS_PER_BUF];
page_cache_sync_readahead(mapping, &ra, NULL, blocknr, BLKS_PER_BUF);
for (i = 0; i < BLKS_PER_BUF; i++) {
for (i = 0; i < BLKS_PER_BUF; i++) {