mm: fix swap_read_folio_zeromap() for large folios with partial zeromap

Patch series "mm: enable large folios swap-in support", v9.

Currently, we support mTHP swapout but not swapin.  This means that once
mTHP is swapped out, it will come back as small folios when swapped in. 
This is particularly detrimental for devices like Android, where more than
half of the memory is in swap.

The lack of mTHP swapin functionality makes mTHP a showstopper in
scenarios that heavily rely on swap.  This patchset introduces mTHP
swap-in support.  It starts with synchronous devices similar to zRAM,
aiming to benefit as many users as possible with minimal changes.


This patch (of 3):

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.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 0ca0c24e3211 ("mm: store zero pages to be swapped out in a bitmap")
Signed-off-by: Barry Song <[email protected]>
Reviewed-by: Yosry Ahmed <[email protected]>
Reviewed-by: Usama Arif <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Chuanhua Han <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gao Xiang <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Kalesh Singh <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Kanchana P Sridhar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions