On Tue, 16 Nov 2021 at 03:20, Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > ---- 在 星期四, 2021-10-07 21:34:19 Miklos Szeredi <miklos@xxxxxxxxxx> 撰写 ---- > > On Thu, 7 Oct 2021 at 15:10, Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote: > > > > However that wasn't what I was asking about. AFAICS ->write_inode() > > > > won't start write back for dirty pages. Maybe I'm missing something, > > > > but there it looks as if nothing will actually trigger writeback for > > > > dirty pages in upper inode. > > > > > > > > > > Actually, page writeback on upper inode will be triggered by overlayfs ->writepages and > > > overlayfs' ->writepages will be called by vfs writeback function (i.e writeback_sb_inodes). > > > > Right. > > > > But wouldn't it be simpler to do this from ->write_inode()? > > > > I.e. call write_inode_now() as suggested by Jan. > > > > Also could just call mark_inode_dirty() on the overlay inode > > regardless of the dirty flags on the upper inode since it shouldn't > > matter and results in simpler logic. > > > > Hi Miklos， > > Sorry for delayed response for this, I've been busy with another project. > > I agree with your suggesion above and further more how about just mark overlay inode dirty > when it has upper inode? This approach will make marking dirtiness simple enough. Are you suggesting that all non-lower overlay inodes should always be dirty? The logic would be simple, no doubt, but there's the cost to walking those overlay inodes which don't have a dirty upper inode, right? Can you quantify this cost with a benchmark? Can be totally synthetic, e.g. lookup a million upper files without modifying them, then call syncfs. Thanks, Miklos
