On Mon, Sep 23, 2024 at 06:17:07PM -0700, Kanchana P Sridhar wrote:
> zswap_store() will now store mTHP and PMD-size THP folios by compressing
The hugepage terminology throughout the patches is a bit convoluted.
There is no real distinction in this code between PMD-size THPs and
sub-PMD-sized mTHPs e.g. In particular, I think "mTHP" made sense when
they were added, to distinguish them from conventional THPs. But using
this term going forward just causes confusion, IMO.
We're going through a big effort in the codebase to call all of these
things simply "folios" - which stands for "one or more pages". If you
want to emphasize the "more than one page", the convention is to call
it a "large folio". (If you need to emphasize that it's PMD size -
which doesn't apply to these patches, but just for the record - the
convention is "pmd-mappable folio".)
So what this patch set does is "support large folios in zswap".
> @@ -1551,51 +1559,63 @@ static bool __maybe_unused zswap_store_page(struct folio *folio, long index,
> return false;
> }
>
> +/*
> + * Modified to store mTHP folios. Each page in the mTHP will be compressed
> + * and stored sequentially.
> + */
This is a changelog, not a code comment ;) Please delete it.
> 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);
> - struct zswap_entry *entry;
> struct obj_cgroup *objcg = NULL;
> struct mem_cgroup *memcg = NULL;
> + struct zswap_pool *pool;
> + bool ret = false;
> + long index;
>
> VM_WARN_ON_ONCE(!folio_test_locked(folio));
> VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
>
> - /* Large folios aren't supported */
> - if (folio_test_large(folio))
> + /* Storing large folios isn't enabled */
> + if (!zswap_mthp_enabled && folio_test_large(folio))
> return false;
>
> if (!zswap_enabled)
> - goto check_old;
> + goto reject;
>
> - /* Check cgroup limits */
> + /*
> + * Check cgroup limits:
> + *
> + * The cgroup zswap limit check is done once at the beginning of an
> + * mTHP store, and not within zswap_store_page() for each page
> + * in the mTHP. We do however check the zswap pool limits at the
Use "folio" and "large folio" as appropriate here and throughout.
