Re: [PATCH v2 00/16] Allow readpage to return a locked page

[Matthew Wilcox <willy@infradead.org>]

On Thu, Oct 15, 2020 at 10:02:42AM +0100, Christoph Hellwig wrote:
> On Fri, Oct 09, 2020 at 03:30:48PM +0100, Matthew Wilcox (Oracle) wrote:
> > Ideally all filesystems would return from ->readpage with the page
> > Uptodate and Locked, but it's a bit painful to convert all the
> > asynchronous readpage implementations to synchronous.  The first 14
> > filesystems converted are already synchronous.  The last two patches
> > convert iomap to synchronous readpage.
> 
> Is it really that bad?  It seems like a lot of the remainig file systems
> use the generic mpage/buffer/nobh helpers.
> 
> But I guess this series is a good first step.

I'm just testing a patch to mpage_readpage():

+++ b/fs/mpage.c
@@ -406,11 +406,17 @@ int mpage_readpage(struct page *page, get_block_t get_block)
                .nr_pages = 1,
                .get_block = get_block,
        };
+       int err;
 
        args.bio = do_mpage_readpage(&args);
-       if (args.bio)
-               mpage_bio_submit(REQ_OP_READ, 0, args.bio);
-       return 0;
+       if (!args.bio)
+               return 0;
+       bio_set_op_attrs(args.bio, REQ_OP_READ, 0);
+       guard_bio_eod(args.bio);
+       err = submit_bio_wait(args.bio);
+       if (!err)
+               err = AOP_UPDATED_PAGE;
+       return err;
 }
 EXPORT_SYMBOL(mpage_readpage);
 

but I'm not looking forward to block_read_full_page().