On Thu, Jan 30, 2020 at 03:53:37PM +0000, Johannes Thumshirn wrote: > On 30/01/2020 14:39, Christoph Hellwig wrote: > > On Thu, Jan 30, 2020 at 01:15:30PM +0100, David Sterba wrote: > >>> Sure but with hch's proposed change to using read_cache_page_gfp() this > >>> doesn't make too much sense anymore at least for the read path. > >>> > >>> Maybe "use page cache for superblock reading"? > >> > >> That works too. We might need a new iteration that summarizes up all the > >> feedback so far, so we have same code to refer to. > > > > Per my question on the second patch: why even use the page cache at > > all. btrfs already caches the value outside the pagecache, so why > > even bother with the page cache overhead? > > > This is what my first version did, alloc_page() and submit_bio() > directly [1]. But reviewers told me to go the route via page cache. I only see your patch at the url, not any reply. What is the issue of not using the page cache? Also you really shoudn't need a separate alloc_page - you should be able to use the already cached superblock as the destination and source of I/O, assuming they are properly aligned (and if not that could be fixed easily).
