Re: [PATCH v2] mm: fix race between MADV_FREE reclaim and blkdev direct IO read

[Minchan Kim <minchan@kernel.org>]

On Tue, Jan 11, 2022 at 12:20:13PM -0800, Minchan Kim wrote:
< snip >
> > > slow path with __gup_longterm_unlocked and set_dirty_pages
> > > for them).
> > > 
> > > This approach would solve other cases where map userspace
> > > pages into kernel space and then write. Since the write
> > > didn't go through with the process's page table, we will
> > > lose the dirty bit in the page table of the process and
> > > it turns out same problem. That's why I'd like to approach
> > > this.
> > > 
> > > If it doesn't work, the other option to fix this specific
> > > case is can't we make pages dirty in advance in DIO read-case?
> > > 
> > > When I look at DIO code, it's already doing in async case.
> > > Could't we do the same thing for the other cases?
> > > I guess the worst case we will see would be more page
> > > writeback since the page becomes dirty unnecessary.
> > 
> > Marking pages dirty after pinning them is a pre-existing area of
> > problems. See the long-running LWN articles about get_user_pages() [1].
> 
> Oh, Do you mean marking page dirty in DIO path is already problems?

                  ^ marking page dirty too late in DIO path

Typo fix.