Re: [RFC PATCH] iomap: generalize IOMAP_INLINE to cover tail-packing case

From: Gao Xiang <hsiangkao@aol.com>
To: "Andreas Grünbacher" <andreas.gruenbacher@gmail.com>
Cc: Chao Yu <yuchao0@huawei.com>,
	Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	linux-xfs@vger.kernel.org,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	Gao Xiang <gaoxiang25@huawei.com>,
	chao@kernel.org
Subject: Re: [RFC PATCH] iomap: generalize IOMAP_INLINE to cover tail-packing case
Date: Thu, 11 Jul 2019 07:42:20 +0800	[thread overview]
Message-ID: <1506e523-109d-7253-ee4b-961c4264781d@aol.com> (raw)
In-Reply-To: <CAHpGcMJ_wPJf8KtF3xMP_28pe4Vq4XozFtmd2EuZ+RTqZKQxLA@mail.gmail.com>

At 2019/7/11 ??????5:50, Andreas Gr??nbacher Wrote:
> At this point, can I ask how important this packing mechanism is to
> you? I can see a point in implementing inline files, which help
> because there tends to be a large number of very small files. But for
> not-so-small files, is saving an extra block really worth the trouble,
> especially given how cheap storage has become?

I would try to answer the above. I think there are several advantages by
using tail-end packing inline:
1) It is more cache-friendly. Considering a file "A" accessed by user
now or recently, we
?????? tend to (1) get more data about "A" (2) leave more data about "A"
according to LRU-like assumption
?????? because it is more likely to be used than the metadata of some other
files "X", especially for files whose
?????? tail-end block is relatively small enough (less than a threshold,
e.g. < 100B just for example);

2) for directories files, tail-end packing will boost up those traversal
performance;

3) I think tail-end packing is a more generic inline, it saves I/Os for
generic cases not just to
?????? save the storage space;

"is saving an extra block really worth the trouble" I dont understand
what exact the trouble is...

Thanks,
Gao Xiang