Question: what happens if writeing back to swap ends in error

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Hi,

What happens when I/O request from swap_writeback() ends in I/O Error ?

swap_writepage() (in mm/page_io.c) sets bio->bi_end_io as end_swap_bio_write().
After I/O ends, bio_endio()->end_swap_bio_write() is called, I think.

If that writeback was end in error, bio-bi_flags's BIO_UPTODATE is cleared.
Then, page is marked with PG_error.
==
static int end_swap_bio_write(struct bio *bio, unsigned int bytes_done, int err)
{
        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct page *page = bio->bi_io_vec[0].bv_page;

        if (bio->bi_size)
                return 1;

        if (!uptodate)
                SetPageError(page);
        end_page_writeback(page);
        bio_put(bio);
        return 0;
}
==
But here, PG_writeback is cleared, anyway.

Now, shrink_list() doesn't handle PG_error.
If the page is not accessed, page's state is !PageDirty() && !PageWriteback()
and SwapCache and on LRU.
Finally, page marked with PG_error is freed by shrink_list() and data in the
page will be lost.

correct ?

-Kame



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