Man page 9 : mpage_writepages

mpage_writepages - walk the list of dirty pages of the given address space & writepage all of them

int mpage_writepages(struct address_space *  mapping , struct writeback_control *  wbc , get_block_t  get_block );

mapping
    address space structure to write

wbc
    subtract the number of written pages from *wbc->nr_to_write

get_block
    the filesystemAqs block mapper function. If this is NULL then use a_ops->writepage. Otherwise, go direct-to-BIO.

This is a library function, which implements the writepages address_space_operation.

If a page is already under I/O, generic_writepages skips it, even if itAqs dirty. This is desirable behaviour for memory-cleaning writeback, but it is INCORRECT for data-integrity system calls such as fsync. fsync and msync need to guarantee that all the data which was dirty at the time the call was made get new I/O started against them. If wbc->sync_mode is WB_SYNC_ALL then we were called for data integrity and we must wait for existing IO to complete.