On 15.01.2019 19:36, Miklos Szeredi wrote: > On Tue, Jan 15, 2019 at 5:14 PM Kirill Tkhai <[email protected]> wrote: >> >> On 15.01.2019 18:39, Miklos Szeredi wrote: >>> On Mon, Nov 26, 2018 at 10:46 AM Kirill Tkhai <[email protected]> wrote: >>>> >>>> It looks like we can optimize old_req page replacement >>>> and avoid copying by simple updating the request's page. >>>> >>>> Signed-off-by: Kirill Tkhai <[email protected]> >>>> --- >>>> fs/fuse/file.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >>>> index c6650c68b31a..83b54b082c86 100644 >>>> --- a/fs/fuse/file.c >>>> +++ b/fs/fuse/file.c >>>> @@ -1778,7 +1778,7 @@ static bool fuse_writepage_in_flight(struct fuse_req >>>> *new_req, >>>> if (old_req->num_pages == 1 && old_req != first_req) { >>>> struct backing_dev_info *bdi = >>>> inode_to_bdi(page->mapping->host); >>>> >>>> - copy_highpage(old_req->pages[0], page); >>>> + swap(old_req->pages[0], page); >>> >>> This would mess up refcounting for all pages involved. need to swap >>> with the temp page in new_req. Fixed version in #for-next. >> >> You are sure, page is just a simple pointer, not struct **page. >> Then we would have had to change fuse_writepage_in_flight() to use ** >> pointer. > > Using a struct page** would still have been broken, not because of > refcounting, but because of putting the wrong page into the request > (we do the temporary copy to avoid some issues with adding the page > cache page directly into the request)
Ok, thanks for the explanation. Kirill
