[PROPOSAL] Implement scatter-gather lists support in UBI and UBIFS

Ezequiel Garcia

Hi all,

This was originally suggested by Artem Bityutskiy; so I'm just putting
up a proposal
by digging his own words from old mails and public discussions.

Once again, apologies for the late submission.
Implement scatter-gather lists support in UBI and UBIFS

; Summary: Implement scatter-gather lists support in UBI and UBIFS

; Proposer: Ezequiel García <ezequiel@...>

== Description ==
Currently UBI and UBIFS seem to allocate a lot vmalloced LEB-sized buffers
on mount time. The reason for this is to "reserve" such memory and prevent
the big allocations from failing at a later point.

This heavily affects the memory footprint in systems using UBIFS.

A possible solution is to implement scatter-gather lists support in UBI
and UBIFS and replace the big (LEB-sized) vmallocations by smaller

While this is a big effort and will only benefit UBIFS, it is expected that
it will help reduce the memory usage in such systems.

In addition, it has the added benefit of addressing another problem.
Some ARM platforms don't support DMA on vmalloc'ed buffers;
using scatter-gather lists the allocated will be quite smaller -O(page)-,
and it will be possible to allocate them on physically contiguous memory
(DMA capable).

These are recurrent issues [1, 2, 3] in the UBI mailing list, and it's
UBI maintainer's
suggested proposal [4].

== Related work ==
As Linus Walleij pointed out [5] the MMC subsystem already implements something
along this lines, and so this work might start by looking at that.

== Scope ==

== Contractor Candidates ==
None yet.

[1] http://lists.infradead.org/pipermail/linux-mtd/2009-August/026817.html
[2] http://lists.infradead.org/pipermail/linux-mtd/2012-November/044982.html
[3] http://lists.infradead.org/pipermail/linux-mtd/2012-October/044586.html
[4] http://lists.infradead.org/pipermail/linux-mtd/2012-November/045140.html
[5] http://lists.infradead.org/pipermail/linux-mtd/2012-October/044608.html

[[Category:Project proposals 2013]]

Ezequiel García, VanguardiaSur

Bird, Tim <Tim.Bird@...>


Thanks for this proposal also. Here is a link to the proposal on the wiki:

-- Tim