> -----Original Message----- > From: Johannes Weiner <hannes@xxxxxxxxxxx> > Sent: Tuesday, October 1, 2024 4:11 AM > To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx; > chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx; > shakeel.butt@xxxxxxxxx; ryan.roberts@xxxxxxx; Huang, Ying > <ying.huang@xxxxxxxxx>; 21cnbao@xxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; > willy@xxxxxxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Feghali, Wajdi K > <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh <vinodh.gopal@xxxxxxxxx> > Subject: Re: [PATCH v10 6/7] mm: zswap: Support large folios in > zswap_store(). > > On Mon, Sep 30, 2024 at 10:32:21PM -0700, Kanchana P Sridhar 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 > > I would change that to > > Originally-by: Ryan Roberts <ryan.roberts@xxxxxxx> > > > Signed-off-by: > > and drop this for now. Thanks Johannes. Sure, this sounds good. Should I post a v11 for just this specific patch which this change, or a v11 for the entire series? > > > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Many thanks! Really appreciate the code review and comments. Thanks, Kanchana
