Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

[Nai Xia]

On Tue, Jun 9, 2009 at 8:47 PM, Wu Fengguang<fengguang.wu@xxxxxxxxx> wrote:
> On Tue, Jun 09, 2009 at 08:17:22PM +0800, Nick Piggin wrote:
>> On Tue, Jun 09, 2009 at 08:15:10PM +0800, Wu Fengguang wrote:
>> > On Tue, Jun 09, 2009 at 06:48:25PM +0800, Nick Piggin wrote:
>> > > On Tue, Jun 09, 2009 at 02:48:55PM +0800, Wu Fengguang wrote:
>> > > > On Mon, Jun 08, 2009 at 10:46:53PM +0800, Nai Xia wrote:
>> > > > > I meant PG_writeback stops writers to index---->struct page mapping.
>> > > >
>> > > > It's protected by the radix tree RCU locks. Period.
>> > > >
>> > > > If you are referring to the reverse mapping: page->mapping is procted
>> > > > by PG_lock. No one should make assumption that it won't change under
>> > > > page writeback.
>> > >
>> > > Well... I think probably PG_writeback should be enough. Phrased another
>> > > way: I think it is a very bad idea to truncate PG_writeback pages out of
>> > > pagecache. Does anything actually do that?
>> >
>> > There shall be no one. OK I will follow that convention..
>> >
>> > But as I stated it is only safe do rely on the fact "no one truncates
>> > PG_writeback pages" in end_writeback_io handlers. And I suspect if
>> > there does exist such a handler, it could be trivially converted to
>> > take the page lock.
>>
>> Well, the writeback submitter first sets writeback, then unlocks
>> the page. I don't think he wants a truncate coming in at that point.
>
> OK. I think we've mostly agreed on the consequences of PG_writeback vs
> truncation. I'll follow the least surprise principle and stop here, hehe.

And thank you both for your time & patience, :-)

Best Regards,
Nai Xia

>
> Thanks,
> Fengguang
>
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