linux-kernel - Re: [RFC PATCH 2/3] mm/filemap: Avoid modifying iocb->ki_flags for AIO in filemap_get

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Message-ID: <aIDy076Sxt544qja@casper.infradead.org>
Date: Wed, 23 Jul 2025 15:33:55 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Chi Zhiling <chizhiling@....com>
Cc: akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Chi Zhiling <chizhiling@...inos.cn>
Subject: Re: [RFC PATCH 2/3] mm/filemap: Avoid modifying iocb->ki_flags for
 AIO in filemap_get_pages()

On Wed, Jul 23, 2025 at 06:18:24PM +0800, Chi Zhiling wrote:
> From: Chi Zhiling <chizhiling@...inos.cn>
> 
> Setting IOCB_NOWAIT in filemap_get_pages() for AIO is only used to
> indicate not to block in the filemap_update_page(), with no other purpose.
> Moreover, in filemap_read(), IOCB_NOWAIT will be set again for AIO.
> 
> Therefore, adding a parameter to the filemap_update_page function to
> explicitly indicate not to block serves the same purpose as indicating
> through iocb->ki_flags, thus avoiding modifications to iocb->ki_flags.
> 
> This patch does not change the original logic and is preparation for the
> next patch.

Passing multiple booleans to a function is an antipattern.
Particularly in this case, since we could just pass iocb->ki_flags
to the function.

But I think there's a less complicated way to do what you want.
Just don't call filemap_update_page() if there are uptodate folios
in the batch:

+++ b/mm/filemap.c
@@ -2616,9 +2616,10 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
                        goto err;
        }
        if (!folio_test_uptodate(folio)) {
-               if ((iocb->ki_flags & IOCB_WAITQ) &&
-                   folio_batch_count(fbatch) > 1)
-                       iocb->ki_flags |= IOCB_NOWAIT;
+               if (folio_batch_count(fbatch) > 1) {
+                       err = -EAGAIN;
+                       goto err;
+               }
                err = filemap_update_page(iocb, mapping, count, folio,
                                          need_uptodate);
                if (err)