On Wed 09-04-14 00:17:59, Jan Kara wrote: > On Sun 23-03-14 15:08:34, Matthew Wilcox wrote: > > +/** > > + * dax_truncate_page - handle a partial page being truncated in a DAX file > > + * @inode: The file being truncated > > + * @from: The file offset that is being truncated to > > + * @get_block: The filesystem method used to translate file offsets to blocks > > + * > > + * Similar to block_truncate_page(), this function can be called by a > > + * filesystem when it is truncating an DAX file to handle the partial page. > > + * > > + * We work in terms of PAGE_CACHE_SIZE here for commonality with > > + * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem > > + * took care of disposing of the unnecessary blocks. Even if the filesystem > > + * block size is smaller than PAGE_SIZE, we have to zero the rest of the page > > + * since the file might be mmaped. > Well, DAX mmap support pretty much relies on PAGE_CACHE_SIZE == block > size (we cannot really map only a part of a physical page directly...). So > the comment seems somewhat misleading. I thought about this for a while and classical IO, truncation etc. could easily work for blocksize < pagesize. And for mmap() you could just use pagecache. Not sure if it's worth the complications though. Anyway we should decide whether we don't care about blocksize < PAGE_CACHE_SIZE at all, or whether we try to make things which can work reasonably easily functional. In that case dax_truncate_page() needs some tweaking because it currently assumes blocksize == PAGE_CACHE_SIZE. Honza > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>