Re: [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area
From: Gioh Kim
Date: Wed Jul 30 2014 - 03:56:45 EST
2014-07-27 ìì 10:01, Theodore Ts'o ì ê:
As follow up, if you want some further discussions about why these
patches should be accepted, it would be good to get some hard data
about why the keeping the ext4 superblock pinned is causing such a
problem for page migation. Can you give us more details about what
the impact is of not having these patches? And how it compres to
other data structures which are currently allocated in the moveable
area and tend to be pinned effectively indefinitely?
I am very sorry to be late. I couldn't access the network for a week.
sb_bread() allocates page from movable area but the reference count of the buffer-head
that manages page should be zero to migrate the page.
Therefore brelase() should be called immediately after sb_bread() such like fat_fill_super().
But ext4 called brelse() when unmount the superblock.
The page cannot be movable until unmount.
CMA/HOTPLUG memory try to move the page but it fails.
If ext4 needs to keep buffer-cache of superblock until unmount,
it should allocated the page from non-movable area (because it can be a long time).
This patch try to do it.
I also sent an email to Jan Kara. Please refer it.
Thank you for your kindness.
Please inform me if you need any information.
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