The quilt patch titled Subject: mm: count zeromap read and set for swapout and swapin has been removed from the -mm tree. Its filename was mm-count-zeromap-read-and-set-for-swapout-and-swapin.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Barry Song <v-songbaohua@xxxxxxxx> Subject: mm: count zeromap read and set for swapout and swapin Date: Wed, 6 Nov 2024 10:19:34 +1300 When the proportion of folios from the zeromap is small, missing their accounting may not significantly impact profiling. However, it's easy to construct a scenario where this becomes an issueâ??for example, allocating 1 GB of memory, writing zeros from userspace, followed by MADV_PAGEOUT, and then swapping it back in. In this case, the swap-out and swap-in counts seem to vanish into a black hole, potentially causing semantic ambiguity. On the other hand, Usama reported that zero-filled pages can exceed 10% in workloads utilizing zswap, while Hailong noted that some app in Android have more than 6% zero-filled pages. Before commit 0ca0c24e3211 ("mm: store zero pages to be swapped out in a bitmap"), both zswap and zRAM implemented similar optimizations, leading to these optimized-out pages being counted in either zswap or zRAM counters (with pswpin/pswpout also increasing for zRAM). With zeromap functioning prior to both zswap and zRAM, userspace will no longer detect these swap-out and swap-in actions. We have three ways to address this: 1. Introduce a dedicated counter specifically for the zeromap. 2. Use pswpin/pswpout accounting, treating the zero map as a standard backend. This approach aligns with zRAM's current handling of same-page fills at the device level. However, it would mean losing the optimized-out page counters previously available in zRAM and would not align with systems using zswap. Additionally, as noted by Nhat Pham, pswpin/pswpout counters apply only to I/O done directly to the backend device. 3. Count zeromap pages under zswap, aligning with system behavior when zswap is enabled. However, this would not be consistent with zRAM, nor would it align with systems lacking both zswap and zRAM. Given the complications with options 2 and 3, this patch selects option 1. We can find these counters from /proc/vmstat (counters for the whole system) and memcg's memory.stat (counters for the interested memcg). For example: $ grep -E 'swpin_zero|swpout_zero' /proc/vmstat swpin_zero 1648 swpout_zero 33536 $ grep -E 'swpin_zero|swpout_zero' /sys/fs/cgroup/system.slice/memory.stat swpin_zero 3905 swpout_zero 3985 This patch does not address any specific zeromap bug, but the missing swpout and swpin counts for zero-filled pages can be highly confusing and may mislead user-space agents that rely on changes in these counters as indicators. Therefore, we add a Fixes tag to encourage the inclusion of this counter in any kernel versions with zeromap. Link: https://lkml.kernel.org/r/20241105211934.5083-1-21cnbao@xxxxxxxxx Fixes: 0ca0c24e3211 ("mm: store zero pages to be swapped out in a bitmap") Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx> Cc: Usama Arif <usamaarif642@xxxxxxxxx> Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx> Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx> Cc: Hailong Liu <hailong.liu@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Cc: Chris Li <chrisl@xxxxxxxxxx> Cc: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Kairui Song <kasong@xxxxxxxxxxx> Cc: Ryan Roberts <ryan.roberts@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/admin-guide/cgroup-v2.rst | 9 +++++++++ include/linux/vm_event_item.h | 2 ++ mm/memcontrol.c | 4 ++++ mm/page_io.c | 16 ++++++++++++++++ mm/vmstat.c | 2 ++ 5 files changed, 33 insertions(+) --- a/Documentation/admin-guide/cgroup-v2.rst~mm-count-zeromap-read-and-set-for-swapout-and-swapin +++ a/Documentation/admin-guide/cgroup-v2.rst @@ -1599,6 +1599,15 @@ The following nested keys are defined. pglazyfreed (npn) Amount of reclaimed lazyfree pages + swpin_zero + Number of pages swapped into memory and filled with zero, where I/O + was optimized out because the page content was detected to be zero + during swapout. + + swpout_zero + Number of zero-filled pages swapped out with I/O skipped due to the + content being detected as zero. + zswpin Number of pages moved in to memory from zswap. --- a/include/linux/vm_event_item.h~mm-count-zeromap-read-and-set-for-swapout-and-swapin +++ a/include/linux/vm_event_item.h @@ -134,6 +134,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS #ifdef CONFIG_SWAP SWAP_RA, SWAP_RA_HIT, + SWPIN_ZERO, + SWPOUT_ZERO, #ifdef CONFIG_KSM KSM_SWPIN_COPY, #endif --- a/mm/memcontrol.c~mm-count-zeromap-read-and-set-for-swapout-and-swapin +++ a/mm/memcontrol.c @@ -431,6 +431,10 @@ static const unsigned int memcg_vm_event PGDEACTIVATE, PGLAZYFREE, PGLAZYFREED, +#ifdef CONFIG_SWAP + SWPIN_ZERO, + SWPOUT_ZERO, +#endif #ifdef CONFIG_ZSWAP ZSWPIN, ZSWPOUT, --- a/mm/page_io.c~mm-count-zeromap-read-and-set-for-swapout-and-swapin +++ a/mm/page_io.c @@ -204,7 +204,9 @@ static bool is_folio_zero_filled(struct static void swap_zeromap_folio_set(struct folio *folio) { + struct obj_cgroup *objcg = get_obj_cgroup_from_folio(folio); struct swap_info_struct *sis = swp_swap_info(folio->swap); + int nr_pages = folio_nr_pages(folio); swp_entry_t entry; unsigned int i; @@ -212,6 +214,12 @@ static void swap_zeromap_folio_set(struc entry = page_swap_entry(folio_page(folio, i)); set_bit(swp_offset(entry), sis->zeromap); } + + count_vm_events(SWPOUT_ZERO, nr_pages); + if (objcg) { + count_objcg_events(objcg, SWPOUT_ZERO, nr_pages); + obj_cgroup_put(objcg); + } } static void swap_zeromap_folio_clear(struct folio *folio) @@ -503,6 +511,7 @@ static void sio_read_complete(struct kio static bool swap_read_folio_zeromap(struct folio *folio) { int nr_pages = folio_nr_pages(folio); + struct obj_cgroup *objcg; bool is_zeromap; /* @@ -517,6 +526,13 @@ static bool swap_read_folio_zeromap(stru if (!is_zeromap) return false; + objcg = get_obj_cgroup_from_folio(folio); + count_vm_events(SWPIN_ZERO, nr_pages); + if (objcg) { + count_objcg_events(objcg, SWPIN_ZERO, nr_pages); + obj_cgroup_put(objcg); + } + folio_zero_range(folio, 0, folio_size(folio)); folio_mark_uptodate(folio); return true; --- a/mm/vmstat.c~mm-count-zeromap-read-and-set-for-swapout-and-swapin +++ a/mm/vmstat.c @@ -1415,6 +1415,8 @@ const char * const vmstat_text[] = { #ifdef CONFIG_SWAP "swap_ra", "swap_ra_hit", + "swpin_zero", + "swpout_zero", #ifdef CONFIG_KSM "ksm_swpin_copy", #endif _ Patches currently in -mm which might be from v-songbaohua@xxxxxxxx are mm-add-per-order-mthp-swpin-counters.patch mm-add-per-order-mthp-swpin-counters-v2.patch