linux-kernel - Re: [PATCH] fs/writeback: convert wbc_account_cgroup

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Message-ID: <94166f32-7ff9-46d2-83c9-4df2a787fe25@kernel.org>
Date: Fri, 11 Oct 2024 16:56:47 +0800
From: Chao Yu <chao@...nel.org>
To: Matthew Wilcox <willy@...radead.org>, Jaegeuk Kim <jaegeuk@...nel.org>
Cc: Chao Yu <chao@...nel.org>,
 "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 Theodore Ts'o <tytso@....edu>, Jonathan Corbet <corbet@....net>,
 Josef Bacik <josef@...icpanda.com>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 "Darrick J . Wong" <djwong@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
 Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
 Christian Brauner <brauner@...nel.org>,
 Andreas Dilger <adilger.kernel@...ger.ca>, Jan Kara <jack@...e.cz>,
 Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
 cgroups@...r.kernel.org, linux-btrfs@...r.kernel.org,
 linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-f2fs-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org,
 mcgrof@...nel.org, gost.dev@...sung.com, linux-doc@...r.kernel.org,
 linux-xfs@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] fs/writeback: convert wbc_account_cgroup_owner to take a
 folio

On 2024/10/1 6:58, Jaegeuk Kim wrote:
> On 09/26, Matthew Wilcox wrote:
>> On Thu, Sep 26, 2024 at 04:01:21PM +0200, Pankaj Raghav (Samsung) wrote:
>>> Convert wbc_account_cgroup_owner() to take a folio instead of a page,
>>> and convert all callers to pass a folio directly except f2fs.
>>>
>>> Convert the page to folio for all the callers from f2fs as they were the
>>> only callers calling wbc_account_cgroup_owner() with a page. As f2fs is
>>> already in the process of converting to folios, these call sites might
>>> also soon be calling wbc_account_cgroup_owner() with a folio directly in
>>> the future.
>>
>> I was hoping for more from f2fs.  I still don't have an answer from them
>> whether they're going to support large folios.  There's all kinds of
>> crud already in these functions like:
>>
>>          f2fs_set_bio_crypt_ctx(bio, fio->page->mapping->host,
>>                          page_folio(fio->page)->index, fio, GFP_NOIO);
>>
>> and this patch is making it worse, not better.  A series of patches
>> which at least started to spread folios throughout f2fs would be better.
>> I think that struct f2fs_io_info should have its page converted to
>> a folio, for example.  Although maybe not; perhaps this structure can
>> carry data which doesn't belong to a folio that came from the page cache.
>> It's very hard to tell because f2fs is so mind-numbingly complex and
>> riddled with stupid abstraction layers.
> 
> Hah, I don't think it's too complex at all tho, there's a somewhat complexity to
> support file-based encryption, compression, and fsverity, which are useful

I agree w/ Jaegeuk.

> for Android users. Well, I don't see any strong needs to support large folio,
> but some requests exist which was why we had to do some conversion.
> 
>>
>> But I don't know what the f2fs maintainers have planned.  And they won't
>> tell me despite many times of asking.

I supported large folio in f2fs by using a hacking way /w iomap fwk, it can
only be enabled in very limited condition, after some seqread tests, I can
see performance gain in server environment, but none in android device, and
in addition, there is a memory leak bug which can cause out-of-memory issue.
Unlucky, I have no slots to dig into these issues recently.

Thanks,