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Date:   Thu, 21 Oct 2021 13:01:30 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Manjong Lee <mj0123.lee@samsung.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        seunghwan.hyun@samsung.com, sookwan7.kim@samsung.com,
        nanich.lee@samsung.com, yt0928.kim@samsung.com,
        junho89.kim@samsung.com, jisoo2146.oh@samsung.com
Subject: Re: [PATCH 1/1] mm: bdi: Initialize bdi_min_ratio when bdi unregister
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References: <CGME20211021072307epcas1p4aa4388c13e71a66e3e1d5f7ee68b5a7f@epcas1p4.samsung.com>
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On Thu, Oct 21, 2021 at 04:16:52AM -0700, Christoph Hellwig wrote:
> On Fri, Oct 22, 2021 at 01:19:43AM +0900, Manjong Lee wrote:
> > Because when sdcard is removed, bdi_min_ratio value will remain.
> > Currently, the only way to reset bdi_ min_ratio is to reboot.
> 
> But bdis that are unregistered are never re-registered.  What is
> the problem you're trying to solve?

The global bdi_min_ratio needs to be adjusted.  See
bdi_set_min_ratio() in mm/page-writeback.c.