From: Gao Xiang <hsiangkao@redhat.com>
To: Chao Yu <yuchao0@huawei.com>
Cc: Martin DEVERA <devik@eaxlabs.cz>,
linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] erofs: fix bio->bi_max_vecs behavior change
Date: Fri, 19 Mar 2021 12:16:21 +0800 [thread overview]
Message-ID: <20210319041621.GB1431129@xiangao.remote.csb> (raw)
In-Reply-To: <dffa941d-63b5-2068-80f4-dd012f520147@huawei.com>
Hi Chao,
On Fri, Mar 19, 2021 at 10:15:18AM +0800, Chao Yu wrote:
> On 2021/3/6 12:04, Gao Xiang wrote:
...
> > + (*last_block + 1 != current_block || !*eblks)) {
>
> Xiang,
>
> I found below function during checking bi_max_vecs usage in f2fs:
>
> /**
> * bio_full - check if the bio is full
> * @bio: bio to check
> * @len: length of one segment to be added
> *
> * Return true if @bio is full and one segment with @len bytes can't be
> * added to the bio, otherwise return false
> */
> static inline bool bio_full(struct bio *bio, unsigned len)
> {
> if (bio->bi_vcnt >= bio->bi_max_vecs)
> return true;
>
> if (bio->bi_iter.bi_size > UINT_MAX - len)
> return true;
>
> return false;
> }
>
> Could you please check that whether it will be better to use bio_full()
> rather than using left-space-in-bio maintained by erofs itself? something
> like:
>
> if (bio && (bio_full(bio, PAGE_SIZE) ||
> /* not continuous */
> (*last_block + 1 != current_block))
>
> I'm thinking we need to decouple bio detail implementation as much as
> possible, to avoid regression whenever bio used/max size definition
> updates, though I've no idea how to fix f2fs case.
Thanks for your suggestion.
Not quite sure I understand the idea... The original problem was that
when EROFS bio_alloc, the number of requested bvec also partially stood
for remaining blocks of the current on-disk extent to limit the read
length. but after that bio behavior change, bi_max_vec could be increased
internally by block layer (e.g. 1 --> 4), so bi_max_vecs is no longer
as what we expect (I mean passed-in). so could cause read request
out-of-bound or hung. That's why I decided to record it manually (never
rely on bio statistics anymore...)
Also btw, AFAIK, Jianan is still investigating to use iomap instead
(mainly resolve tail-packing inline path). And I'm also busy in big
pcluster and LZMA new features for the next cycle. So I think we might
leave it just as is and it would be replaced with iomap in the future.
Thanks,
Gao Xiang
>
> Let me know if you have other concern.
>
> Thanks,
prev parent reply other threads:[~2021-03-19 4:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210306033109.28466-1-hsiangkao.ref@aol.com>
2021-03-06 3:31 ` [PATCH] erofs: fix bio->bi_max_vecs behavior change Gao Xiang via Linux-erofs
2021-03-06 4:04 ` [PATCH v2] " Gao Xiang via Linux-erofs
2021-03-08 1:29 ` Chao Yu
2021-03-08 2:36 ` Gao Xiang
2021-03-08 2:52 ` Chao Yu
2021-03-08 3:01 ` Gao Xiang
2021-03-19 2:15 ` Chao Yu
2021-03-19 4:16 ` Gao Xiang [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210319041621.GB1431129@xiangao.remote.csb \
--to=hsiangkao@redhat.com \
--cc=devik@eaxlabs.cz \
--cc=linux-erofs@lists.ozlabs.org \
--cc=linux-kernel@vger.kernel.org \
--cc=yuchao0@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).