ubifs:questions about this filesystem

ubifs:questions about this filesystem

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Hi,MTD lists
I've got two questions about ubifs listed below,
1. If I write a file to the filesystem, dose it go to a new block or the same block last written file goes?
2. What's the priority of GC thread? If GC thread is working background, what effect will it bring to other working threads in my embedded system? Can other threads be blocked?

Best Regards,
Andy

Re: ubifs:questions about this filesystem

[Richard Weinberger]

Hi!

On Wed, Jun 22, 2016 at 4:13 PM, 辉少 <wang502742203@qq.com> wrote:
> Hi,MTD lists
> I've got two questions about ubifs listed below,
> 1. If I write a file to the filesystem, dose it go to a new block or the same block last written file goes?

UBIFS tries to fill up LEBs as much as possible. Allocating a new LEB
for every new file would be deadly.

> 2. What's the priority of GC thread? If GC thread is working background, what effect will it bring to other working threads in my embedded system? Can other threads be blocked?

Strictly speaking there is only a background thread to do many things.
GC can happen in many contexts.
The background thread is kthread with default priority.

-- 
Thanks,
//richard

Re: 回复：ubifs:questions about this filesystem

[Richard Weinberger]

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Am 22.06.2016 um 16:43 schrieb »ÔÉÙ:
> As for the second question, I mean if ubifs background is collecting garbage,meanwhile my embeded system is doing another thing, will GC thread affect the performance of "doing another thing"?

Please start unsing reply-all.
Sure will it as every thread on a multithreaded OS does...

Thanks,
//richard

Re: 回复：ubifs:questions about this filesystem

[Richard Weinberger]

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Hi!

Am 22.06.2016 um 17:26 schrieb »ÔÉÙ:
> Thank you for kind reply.
> 
> 1. As you said just now"there is only a background thread to do many things",  dose "many things" include both GC and synchronizing data?

I said GC can happen in many contexts. Also in the calling one.
To figure what the background thread exactly does see function ubifs_bg_thread().

> 2. If I write a file(1 KB) to ubifs mounted in 34MiB mtd, can i write 34,000 times or 34000/4 times(the real disk usage of a 1KB file is 4KB)£¿

The minimal file size on UBIFS is 4KiB. You can also not use all 34MiB, since UBIFS needs some LEBs for the journal, free space accounting,
master nodes, etc...

Thanks,
//richard