Re: + filemap-make-the-accounting-of-thrashing-more-consistent.patch added to mm-unstable branch

[CGEL]

We have discussed related question before. See:
https://lore.kernel.org/all/Yio17pXawRuuVJFO@xxxxxxxxxxx/
The problem is that there is no suitable place to measure pagecache thrashing
in fs level likes swap_readpage(). We have to measure it in folio_wait_bit_common().

If we measure swap thrashing just in swap_readpage(), we will miss pagecache
thrashing. If we measure swap thrashing in swap_readpage(), and measure 
pagecache thrashing in folio_wait_bit_common(), it will be rerpeated calculation.

So this patch is not perfect and it works. If one day we solve the problem of
measure thrashing in folio_wait_bit_common(), we may improve this patch correspond.

Thanks.