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Date: Tue, 23 Jan 2024 09:40:29 +0100
From: Christoph Hellwig <hch@lst.de>
To: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	virtualization@lists.linux.dev
Subject: Re: [PATCH 02/15] block: refactor disk_update_readahead
Message-ID: <20240123084029.GA29041@lst.de>
References: <20240122173645.1686078-1-hch@lst.de> <20240122173645.1686078-3-hch@lst.de> <96007133-162c-4fff-9343-dd88ca520aa7@kernel.org>
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On Tue, Jan 23, 2024 at 01:41:05PM +0900, Damien Le Moal wrote:
> > +{
> > +	/*
> > +	 * For read-ahead of large files to be effective, we need to read ahead
> > +	 * at least twice the optimal I/O size.
> > +	 */
> > +	bdi->ra_pages = max(lim->io_opt * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
> 
> Nit: while at it, you could replace that division by PAGE_SIZE with a right
> shift by PAGE_SHIFT.

I don't really see the point, this is everything but a fast path,
and for simple constant divisions compilers aren't actually bad at
doing optimizations.