Re: [PATCH v9 1/3] mm: Fix swap_read_folio_zeromap() for large folios with partial zeromap

[Usama Arif]

On 09/09/2024 00:21, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
> 
> There could be a corner case where the first entry is non-zeromap,
> but a subsequent entry is zeromap. In this case, we should not
> let swap_read_folio_zeromap() return false since we will still
> read corrupted data.
> 
> Additionally, the iteration of test_bit() is unnecessary and
> can be replaced with bitmap operations, which are more efficient.
> 
> We can adopt the style of swap_pte_batch() and folio_pte_batch() to
> introduce swap_zeromap_batch() which seems to provide the greatest
> flexibility for the caller. This approach allows the caller to either
> check if the zeromap status of all entries is consistent or determine
> the number of contiguous entries with the same status.
> 
> Since swap_read_folio() can't handle reading a large folio that's
> partially zeromap and partially non-zeromap, we've moved the code
> to mm/swap.h so that others, like those working on swap-in, can
> access it.
> 
> Fixes: 0ca0c24e3211 ("mm: store zero pages to be swapped out in a bitmap")
> Cc: Usama Arif <usamaarif642@xxxxxxxxx>
> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>

Reviewed-by: Usama Arif <usamaarif642@xxxxxxxxx>