On Thu, Aug 15, 2019 at 08:30:43AM +0800, wangyan wrote: [] > > I found that the judgement statement 'if (!TestSetPageDirty(page))' always > true in function '__set_page_dirty_nobuffers', it will waste much time > to mark inode dirty, no one page is dirty when write it the second time. > The buffer write stack: > fuse_file_write_iter > ->fuse_cache_write_iter > ->generic_file_write_iter > ->__generic_file_write_iter > ->generic_perform_write > ->fuse_write_end > ->set_page_dirty > ->__set_page_dirty_nobuffers > > The reason for 'if (!TestSetPageDirty(page))' always true may be the pdflush > process will clean the page's dirty flags in clear_page_dirty_for_io(), > and call fuse_writepages_send() to flush all pages to the disk of the host. > So when the page is written the second time, it always not dirty. > The pdflush stack for fuse: > pdflush > ->... > ->do_writepages > ->fuse_writepages > ->write_cache_pages // will clear all page's dirty flags > ->clear_page_dirty_for_io // clear page's dirty flags > ->fuse_writepages_send // write all pages to the host, but > don't wait the result > Why not wait for getting the result of writing back pages to the host > before cleaning all page's dirty flags? > As my understanding, I personally think there's nothing wrong with the above process from your words above. Thanks, Gao Xiang > As for 9p, pdflush will call clear_page_dirty_for_io() to clean the page's > dirty flags. Then call p9_client_write() to write the page to the host, > waiting for the result, and then flush the next page. In this case, buffer > write of 9p will hit the dirty page many times before it is being write > back to the host by pdflush process. > The pdflush stack for 9p: > pdflush > ->... > ->do_writepages > ->generic_writepages > ->write_cache_pages > ->clear_page_dirty_for_io // clear page's dirty flags > ->__writepage > ->v9fs_vfs_writepage > ->v9fs_vfs_writepage_locked > ->p9_client_write // it will get the writing back > page's result > > > According to the test result, is the handling method of 9p for page writing > back more reasonable than virtiofs? > > Thanks, > Yan Wang >
