On Mon, Sep 23, 2024 at 6:17 PM Kanchana P Sridhar
<kanchana.p.sridhar@xxxxxxxxx> wrote:
>
> Added a new procedure zswap_delete_stored_offsets() that can be
> called to delete stored offsets in a folio in case zswap_store()
> fails or zswap is disabled.
I don't see the value in this helper. It will get called in one place
AFAICT, and it is a bit inconsistent that we have to explicitly loop
in zswap_store() to store pages, but the loop to delete pages upon
failure is hidden in the helper.
I am not against adding a trivial zswap_tree_delete() helper (or
similar) that calls xa_erase() and zswap_entry_free() to match
zswap_tree_store() if you prefer that.
>
> Refactored the code in zswap_store() that handles these cases,
> to call zswap_delete_stored_offsets().
>
> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> ---
> mm/zswap.c | 33 ++++++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index fd35a81b6e36..9bea948d653e 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1435,8 +1435,37 @@ static bool zswap_store_entry(struct xarray *tree,
> return true;
> }
>
> +/*
> + * If the zswap store fails or zswap is disabled, we must invalidate the
> + * possibly stale entries which were previously stored at the offsets
> + * corresponding to each page of the folio. Otherwise, writeback could
> + * overwrite the new data in the swapfile.
> + *
> + * This is called after the store of an offset in a large folio has failed.
> + * All zswap entries in the folio must be deleted. This helps make sure
> + * that a swapped-out mTHP is either entirely stored in zswap, or entirely
> + * not stored in zswap.
> + *
> + * This is also called if zswap_store() is invoked, but zswap is not enabled.
> + * All offsets for the folio are deleted from zswap in this case.
> + */
> +static void zswap_delete_stored_offsets(struct xarray *tree,
> + pgoff_t offset,
> + long nr_pages)
> +{
> + struct zswap_entry *entry;
> + long i;
> +
> + for (i = 0; i < nr_pages; ++i) {
> + entry = xa_erase(tree, offset + i);
> + if (entry)
> + zswap_entry_free(entry);
> + }
> +}
> +
> bool zswap_store(struct folio *folio)
> {
> + long nr_pages = folio_nr_pages(folio);
> swp_entry_t swp = folio->swap;
> pgoff_t offset = swp_offset(swp);
> struct xarray *tree = swap_zswap_tree(swp);
> @@ -1541,9 +1570,7 @@ bool zswap_store(struct folio *folio)
> * possibly stale entry which was previously stored at this offset.
> * Otherwise, writeback could overwrite the new data in the swapfile.
> */
> - entry = xa_erase(tree, offset);
> - if (entry)
> - zswap_entry_free(entry);
> + zswap_delete_stored_offsets(tree, offset, nr_pages);
> return false;
> }
>
> --
> 2.27.0
>
