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From: Christoph Hellwig <hch@infradead.org>
To: Liang Chen <liangchen.linux@gmail.com>
Cc: colyli@suse.de, kent.overstreet@gmail.com,
	linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org
Subject: Re: [PATCH 2/2] [PATCH] bcache: __write_super to handle page sizes other than 4k
Date: Fri, 6 Dec 2019 01:23:36 -0800	[thread overview]
Message-ID: <20191206092336.GA7650@infradead.org> (raw)
In-Reply-To: <1575622543-22470-2-git-send-email-liangchen.linux@gmail.com>

On Fri, Dec 06, 2019 at 04:55:43PM +0800, Liang Chen wrote:
> __write_super assumes super block data starts at offset 0 of the page
> read in with __bread from read_super, which is not true when page size
> is not 4k. We encountered the issue on system with 64K page size - commonly
>  seen on aarch64 architecture.
> 
> Instead of making any assumption on the offset of the data within the page,
> this patch calls __bread again to locate the data. That should not introduce
> an extra io since the page has been held when it's read in from read_super,
> and __write_super is not on performance critical code path.

No need to use buffer heads here, you can just use offset_in_page
to calculate the offset.  Similarly I think the read side shouldn't
use buffer heads either (it is the only use of buffer heads in bcache!),
a siple read_cache_page should be all that is needed.

  reply	other threads:[~2019-12-06  9:23 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-06  8:55 [PATCH 1/2] [PATCH] bcache: cached_dev_free needs to put the sb page Liang Chen
2019-12-06  8:55 ` [PATCH 2/2] [PATCH] bcache: __write_super to handle page sizes other than 4k Liang Chen
2019-12-06  9:23   ` Christoph Hellwig [this message]
2019-12-06 11:23     ` Liang C
2019-12-06  9:44   ` Coly Li
2019-12-06 11:22     ` Liang C
2019-12-09  7:37     ` Christoph Hellwig
2019-12-09  9:52       ` Coly Li
2019-12-09 10:21         ` Liang C
2019-12-06  9:27 ` [PATCH 1/2] [PATCH] bcache: cached_dev_free needs to put the sb page Christoph Hellwig
2019-12-06 11:27   ` Liang C
2019-12-06  9:42 ` Coly Li
2019-12-06 23:08 ` Eric Wheeler

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