Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may get wrongly discarded

[Minchan Kim]

On Fri, Mar 13, 2009 at 5:15 PM, KOSAKI Motohiro
<kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
>> > > > Â Â Â Â The ramfs stuff is rather icky in that it adds the pages to the aging
>> > > > Â Â Â Â list, marks them dirty, but does not provide a writeout method.
>> > > >
>> > > > Â Â Â Â This will make the paging code scan over them (continuously) trying to
>> > > > Â Â Â Â clean them, failing that (lack of writeout method) and putting them back
>> > > > Â Â Â Â on the list.
>> > > >
>> > > > Not requiring the pages to be added to the LRU would be a really good idea.
>> > > > They are not discardable, be it in MMU or NOMMU mode, except when the inode
>> > > > itself is discarded.
>> > >
>> > > Yep, these pages shouldn't be on the LRU at all. ÂI guess that will
>> > > require some tweaks to core filemap.c code.
>> >
>> > IMHO, UNEVICTABLE_LRU already does lru isolation.
>> > only rest prblem is, getting rid of "depends on MMU" line in mm/Kconfig.
>> >
>> > Am I missing anything?
>>
>> Yes, the need to take something off that shouldn't be there to begin
>> with.
>
> In past unevictable lru discussion, we discuss the same thing.
> at that time, we found two reason of unevictable lru is better than
> completely taking off.
>
> (1) page migration code depend on the page stay on lru.
> (2) "taking off at reclaim time" can avoid adding lock to fastpath.
> Â Âanyway, complely removing from lru need something lock.
> Â Âwe disliked it at that time

Can you explain this issue more detail when you are in convenience, please ?

> So, I think it is still true.
> Of cource, better cool solution is always welcome :)
>
>
>
>
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-- 
Kinds regards,
Minchan Kim
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