linux-ext4 - ext4: how to make sure the LBA contiguous allocation across a set of files

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Message-ID: <0e5ffd9bb29b018b2ed574381d194c4e7506f91b.camel@gmail.com>
Date:   Mon, 28 Sep 2020 19:49:41 +0200
From:   christopher lee <christopher.lee.eu@...il.com>
To:     linux-ext4@...r.kernel.org
Subject: ext4: how to make sure the LBA contiguous  allocation across a set
 of  files

Hallo
I am recently encountering an issue with the ext4 usage case. I want
not only sequentially LBA allocation in a single file, but also expect
that the LBA sequential allocation between the two files, which means
that the last LBA of the previous file should be adjacent to the first
LAB of the block of the next file.

But from my testing, the sequential LBA of block allocation is easily
met, but the LBA sequential allocation between files is not to ext4.
The gab in LBA between two seq write (two files) is very huge,
sometimes the gap is over 2GB space. I notice ext4 never allocates the
LBA of the block between two files sequentially on my usage case.

who knows the reason of this? and if there is a configuration of ext4
related to this scenario? 
or please tell me which ext4 function I should study, and see if I can
find the reason.

thanks in advance for any suggestions.

Thanks,
Lee