linux-kernel - Re: [PATCH] mm/filemap: invalidating pages is still necessary when io with IOCB

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Date: Thu, 23 May 2024 13:08:02 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Liu Wei <liuwei09@...tc.cn>
Cc: willy@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/filemap: invalidating pages is still necessary when
 io with IOCB_NOWAIT

On Mon, 13 May 2024 21:23:39 +0800 Liu Wei <liuwei09@...tc.cn> wrote:

> After commit (6be96d3ad3 fs: return if direct I/O will trigger writeback),
> when we issuing AIO with direct I/O and IOCB_NOWAIT on a block device, the
> process context will not be blocked.
> 
> However, if the device already has page cache in memory, EAGAIN will be
> returned. And even when trying to reissue the AIO with direct I/O and
> IOCB_NOWAIT again, we consistently receive EAGAIN.
> 
> Maybe a better way to deal with it: filemap_fdatawrite_range dirty pages
> with WB_SYNC_NONE flag, and invalidate_mapping_pages unmapped pages at
> the same time.

Can't userspace do this?  If EAGAIN, sync the fd and retry the IO?