| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <067039c2-5656-40b5-ab6e-a2325e3a9f4e@linux.dev>
Date: Wed, 6 Nov 2024 10:52:31 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>,
Nhat Pham <nphamcs@...il.com>, Usama Arif <usamaarif642@...il.com>,
Yosry Ahmed <yosryahmed@...gle.com>, Hailong Liu <hailong.liu@...o.com>,
Johannes Weiner <hannes@...xchg.org>, David Hildenbrand <david@...hat.com>,
Hugh Dickins <hughd@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Shakeel Butt <shakeel.butt@...ux.dev>, Andi Kleen <ak@...ux.intel.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>, Chris Li <chrisl@...nel.org>,
"Huang, Ying" <ying.huang@...el.com>, Kairui Song <kasong@...cent.com>,
Ryan Roberts <ryan.roberts@....com>
Subject: Re: [PATCH v3] mm: count zeromap read and set for swapout and swapin
On 2024/11/6 05:19, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
>
> 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 issue—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.
>
> Fixes: 0ca0c24e3211 ("mm: store zero pages to be swapped out in a bitmap")
> Reviewed-by: Nhat Pham <nphamcs@...il.com>
> Cc: Usama Arif <usamaarif642@...il.com>
> Cc: Chengming Zhou <chengming.zhou@...ux.dev>
> Cc: Yosry Ahmed <yosryahmed@...gle.com>
> Cc: Hailong Liu <hailong.liu@...o.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
> Cc: Shakeel Butt <shakeel.butt@...ux.dev>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Chris Li <chrisl@...nel.org>
> Cc: "Huang, Ying" <ying.huang@...el.com>
> Cc: Kairui Song <kasong@...cent.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
Looks good to me!
Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
Thanks.
> ---
> -v3:
> * collected Nhat's reviewed-by, thanks!
> * refine doc per Usama and David, thanks!
> * refine changelog
>
> 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(+)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index db3799f1483e..13736a94edfd 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/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.
>
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index aed952d04132..f70d0958095c 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -134,6 +134,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> #ifdef CONFIG_SWAP
> SWAP_RA,
> SWAP_RA_HIT,
> + SWPIN_ZERO,
> + SWPOUT_ZERO,
> #ifdef CONFIG_KSM
> KSM_SWPIN_COPY,
> #endif
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5e44d6e7591e..7b3503d12aaf 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -441,6 +441,10 @@ static const unsigned int memcg_vm_event_stat[] = {
> PGDEACTIVATE,
> PGLAZYFREE,
> PGLAZYFREED,
> +#ifdef CONFIG_SWAP
> + SWPIN_ZERO,
> + SWPOUT_ZERO,
> +#endif
> #ifdef CONFIG_ZSWAP
> ZSWPIN,
> ZSWPOUT,
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 5d9b6e6cf96c..4b4ea8e49cf6 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -204,7 +204,9 @@ static bool is_folio_zero_filled(struct folio *folio)
>
> 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(struct folio *folio)
> 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)
> @@ -507,6 +515,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
> static bool swap_read_folio_zeromap(struct folio *folio)
> {
> int nr_pages = folio_nr_pages(folio);
> + struct obj_cgroup *objcg;
> bool is_zeromap;
>
> /*
> @@ -521,6 +530,13 @@ static bool swap_read_folio_zeromap(struct folio *folio)
> 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;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 22a294556b58..c8ef7352f9ed 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1418,6 +1418,8 @@ const char * const vmstat_text[] = {
> #ifdef CONFIG_SWAP
> "swap_ra",
> "swap_ra_hit",
> + "swpin_zero",
> + "swpout_zero",
> #ifdef CONFIG_KSM
> "ksm_swpin_copy",
> #endif
Powered by blists - more mailing lists