linux-kernel - Re: [PATCH v3 2/2] virtiofs: use GFP_NOFS when enqueuing request through kworker

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Date: Fri, 10 May 2024 13:19:10 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Hou Tao <houtao@...weicloud.com>
Cc: linux-fsdevel@...r.kernel.org, Vivek Goyal <vgoyal@...hat.com>, 
	Stefan Hajnoczi <stefanha@...hat.com>, Bernd Schubert <bernd.schubert@...tmail.fm>, 
	"Michael S . Tsirkin" <mst@...hat.com>, Matthew Wilcox <willy@...radead.org>, 
	Benjamin Coddington <bcodding@...hat.com>, linux-kernel@...r.kernel.org, 
	virtualization@...ts.linux.dev, houtao1@...wei.com
Subject: Re: [PATCH v3 2/2] virtiofs: use GFP_NOFS when enqueuing request
 through kworker

On Fri, 26 Apr 2024 at 16:38, Hou Tao <houtao@...weicloud.com> wrote:
>
> From: Hou Tao <houtao1@...wei.com>
>
> When invoking virtio_fs_enqueue_req() through kworker, both the
> allocation of the sg array and the bounce buffer still use GFP_ATOMIC.
> Considering the size of the sg array may be greater than PAGE_SIZE, use
> GFP_NOFS instead of GFP_ATOMIC to lower the possibility of memory
> allocation failure and to avoid unnecessarily depleting the atomic
> reserves. GFP_NOFS is not passed to virtio_fs_enqueue_req() directly,
> GFP_KERNEL and memalloc_nofs_{save|restore} helpers are used instead.

Makes sense.

However, I don't understand why the GFP_NOFS behavior is optional. It
should work when queuing the request for the first time as well, no?

Thanks,
Miklos