From: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: "dsterba@suse.cz" <dsterba@suse.cz>,
David Sterba <dsterba@suse.com>,
Nikolay Borisov <nborisov@suse.com>,
"linux-btrfs @ vger . kernel . org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH v3 0/5] btrfs: remove buffer heads form superblock handling
Date: Thu, 30 Jan 2020 16:09:45 +0000 [thread overview]
Message-ID: <DM5PR0401MB3591C0E5FE103FF1142005099B040@DM5PR0401MB3591.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20200130155616.GA14682@infradead.org
On 30/01/2020 16:56, Christoph Hellwig wrote:
> On Thu, Jan 30, 2020 at 03:53:37PM +0000, Johannes Thumshirn wrote:
>> On 30/01/2020 14:39, Christoph Hellwig wrote:
>>> On Thu, Jan 30, 2020 at 01:15:30PM +0100, David Sterba wrote:
>>>>> Sure but with hch's proposed change to using read_cache_page_gfp() this
>>>>> doesn't make too much sense anymore at least for the read path.
>>>>>
>>>>> Maybe "use page cache for superblock reading"?
>>>>
>>>> That works too. We might need a new iteration that summarizes up all the
>>>> feedback so far, so we have same code to refer to.
>>>
>>> Per my question on the second patch: why even use the page cache at
>>> all. btrfs already caches the value outside the pagecache, so why
>>> even bother with the page cache overhead?
>>>
>> This is what my first version did, alloc_page() and submit_bio()
>> directly [1]. But reviewers told me to go the route via page cache.
>
> I only see your patch at the url, not any reply. What is the issue
> of not using the page cache? Also you really shoudn't need a separate
> alloc_page - you should be able to use the already cached superblock
> as the destination and source of I/O, assuming they are properly aligned
> (and if not that could be fixed easily).
>
Care to elaborate? Who would have cached the superblock, when we haven't
mounted the FS yet.
So here's the answer from that thread:
"IIRC we had some funny bugs when mount and device scan (udev) raced
just after mkfs, the page cache must be used so there's no way to read
stale data."
https://lore.kernel.org/linux-btrfs/20200117151352.GK3929@twin.jikos.cz/
next prev parent reply other threads:[~2020-01-30 16:09 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 15:59 [PATCH v3 0/5] btrfs: remove buffer heads form superblock handling Johannes Thumshirn
2020-01-27 15:59 ` [PATCH v3 1/5] btrfs: remove buffer heads from super block reading Johannes Thumshirn
2020-01-28 11:47 ` Christoph Hellwig
2020-01-30 10:12 ` Johannes Thumshirn
2020-01-27 15:59 ` [PATCH v3 2/5] btrfs: remove use of buffer_heads from superblock writeout Johannes Thumshirn
2020-01-28 11:52 ` Christoph Hellwig
2020-01-27 15:59 ` [PATCH v3 3/5] btrfs: remove btrfsic_submit_bh() Johannes Thumshirn
2020-01-27 15:59 ` [PATCH v3 4/5] btrfs: remove buffer_heads from btrfsic_process_written_block() Johannes Thumshirn
2020-01-27 15:59 ` [PATCH v3 5/5] btrfs: remove buffer_heads form superblock mirror integrity checking Johannes Thumshirn
2020-01-29 14:25 ` [PATCH v3 0/5] btrfs: remove buffer heads form superblock handling David Sterba
2020-01-30 11:23 ` Johannes Thumshirn
2020-01-30 12:15 ` David Sterba
2020-01-30 13:39 ` Christoph Hellwig
2020-01-30 15:53 ` Johannes Thumshirn
2020-01-30 15:56 ` Christoph Hellwig
2020-01-30 16:09 ` Johannes Thumshirn [this message]
2020-01-30 16:15 ` Christoph Hellwig
2020-01-30 16:16 ` David Sterba
2020-01-31 13:43 ` Johannes Thumshirn
2020-02-03 8:29 ` Christoph Hellwig
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