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SubjectRe: [f2fs-dev] [PATCH] f2fs: clear cold data flag if IO is not counted
On 10/16, Chao Yu wrote:
> On 2018/10/16 7:08, Jaegeuk Kim wrote:
> > On 10/15, Chao Yu wrote:
> >> On 2018/10/11 5:22, Jaegeuk Kim wrote:
> >>> If we clear the cold data flag out of the writeback flow, we can miscount
> >>> -1 by end_io.
> >>
> >> I didn't get it, which count do you mean?
> >
> > It's the number of dirty pages.
> >
> > Balancing F2FS Async:
> > - IO (CP: 1, Data: -1, Flush: ( 0 0 1), Discard: ( 0 129304)) cmd: 0 undiscard: 0
> >
>
> So I guess the race should be:
>
> GC thread: IRQ
> - move_data_page()
> - set_page_dirty()
> - clear_cold_data()
> - f2fs_write_end_io()
> - type = WB_DATA_TYPE(page);
> here, we get wrong type
> - dec_page_count(sbi, type);
> - f2fs_wait_on_page_writeback()
>
> How about relocate wait_writeback & set_page_dirty to avoid above race:

Well, wait_on_stable_page() doesn't guarantee its end_io. So, I'm not sure
this is the only case.

>
> move_data_page()
>
> retry:
> f2fs_wait_on_page_writeback(page, DATA, true);
> set_page_dirty(page);
>
> Thanks,
>
> >>
> >> Thanks,
> >>
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> >>> ---
> >>> fs/f2fs/data.c | 4 ----
> >>> 1 file changed, 4 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>> index 29a9d3b8f709..4102799b5558 100644
> >>> --- a/fs/f2fs/data.c
> >>> +++ b/fs/f2fs/data.c
> >>> @@ -2636,10 +2636,6 @@ static int f2fs_set_data_page_dirty(struct page *page)
> >>> if (!PageUptodate(page))
> >>> SetPageUptodate(page);
> >>>
> >>> - /* don't remain PG_checked flag which was set during GC */
> >>> - if (is_cold_data(page))
> >>> - clear_cold_data(page);
> >>> -
> >>> if (f2fs_is_atomic_file(inode) && !f2fs_is_commit_atomic_write(inode)) {
> >>> if (!IS_ATOMIC_WRITTEN_PAGE(page)) {
> >>> f2fs_register_inmem_page(inode, page);
> >>>
> >
> > .
> >

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