On Mon, Sep 30, 2024 at 10:37 PM Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> wrote: > > zswap_store() will store large folios by compressing them page by page. > > This patch provides a sequential implementation of storing a large folio > in zswap_store() by iterating through each page in the folio to compress > and store it in the zswap zpool. > > zswap_store() calls the newly added zswap_store_page() function for each > page in the folio. zswap_store_page() handles compressing and storing each > page. > > We check the global and per-cgroup limits once at the beginning of > zswap_store(), and only check that the limit is not reached yet. This is > racy and inaccurate, but it should be sufficient for now. We also obtain > initial references to the relevant objcg and pool to guarantee that > subsequent references can be acquired by zswap_store_page(). A new function > zswap_pool_get() is added to facilitate this. > > If these one-time checks pass, we compress the pages of the folio, while > maintaining a running count of compressed bytes for all the folio's pages. > If all pages are successfully compressed and stored, we do the cgroup > zswap charging with the total compressed bytes, and batch update the > zswap_stored_pages atomic/zswpout event stats with folio_nr_pages() once, > before returning from zswap_store(). > > If an error is encountered during the store of any page in the folio, > all pages in that folio currently stored in zswap will be invalidated. > Thus, a folio is either entirely stored in zswap, or entirely not stored > in zswap. > > The most important value provided by this patch is it enables swapping out > large folios to zswap without splitting them. Furthermore, it batches some > operations while doing so (cgroup charging, stats updates). > > This patch also forms the basis for building compress batching of pages in > a large folio in zswap_store() by compressing up to say, 8 pages of the > folio in parallel in hardware using the Intel In-Memory Analytics > Accelerator (Intel IAA). > > This change reuses and adapts the functionality in Ryan Roberts' RFC > patch [1]: > > "[RFC,v1] mm: zswap: Store large folios without splitting" > > [1] https://lore.kernel.org/linux-mm/20231019110543.3284654-1-ryan.roberts@xxxxxxx/T/#u > > Co-developed-by: Ryan Roberts > Signed-off-by: > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
