Messages in this thread | | | Date | Wed, 30 Jul 2014 16:56:27 +0900 | From | Gioh Kim <> | Subject | Re: [PATCH 0/2] new API to allocate buffer-cache for superblock in non-movable area |
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2014-07-27 오전 10:01, Theodore Ts'o 쓴 글: > Gioh, > > 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? > > Thanks, > > - Ted >
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.
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