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Date: Tue, 7 Apr 2026 07:52:47 +0200
From: Christoph Hellwig <hch@lst.de>
To: Naman Jain <namjain@linux.microsoft.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Logan Gunthorpe <logang@deltatee.com>, linux-kernel@vger.kernel.org,
	linux-block@vger.kernel.org,
	Saurabh Sengar <ssengar@linux.microsoft.com>,
	Long Li <longli@microsoft.com>,
	Michael Kelley <mhklinux@outlook.com>
Subject: Re: [PATCH 2/2] block: allow different-pgmap pages as separate
 bvecs in bio_add_page
Message-ID: <20260407055247.GA6405@lst.de>
References: <20260401082329.1602328-1-namjain@linux.microsoft.com> <20260401082329.1602328-3-namjain@linux.microsoft.com> <20260401140850.GC21703@lst.de> <70c82c3a-d135-4877-ab46-c15d329815f5@linux.microsoft.com> <20260402053057.GA11783@lst.de> <d48427c2-9aa3-42a2-a8d7-43a7a3b3b685@linux.microsoft.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

> -               if (!zone_device_pages_have_same_pgmap(bv->bv_page, page))
> +               if (!zone_device_pages_compatible(bv->bv_page, page))
>                         return 0;
> -
> -               if (bvec_try_merge_hw_page(q, bv, page, len, offset)) {
> +               if (zone_device_pages_have_same_pgmap(bv->bv_page, page) &&
> +                   bvec_try_merge_hw_page(q, bv, page, len, offset)) {

We still can't merge merge pages with different P2P pgmaps into the
same request.

So the zone_device_pages_have_same_pgmap check should go into
zone_device_pages_compatible and we need to stop building the bio
as well in that case.