linux-kernel - Re: [PATCH v3 6/7] mm, swap: remove swap slot cache

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Message-ID: <20250428135252.25453B17-hca@linux.ibm.com>
Date: Mon, 28 Apr 2025 15:52:52 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Chris Li <chrisl@...nel.org>, Barry Song <v-songbaohua@...o.com>,
        Hugh Dickins <hughd@...gle.com>, Yosry Ahmed <yosryahmed@...gle.com>,
        "Huang, Ying" <ying.huang@...ux.alibaba.com>,
        Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 6/7] mm, swap: remove swap slot cache

Hi Kairui,

On Fri, Mar 14, 2025 at 12:59:34AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> Slot cache is no longer needed now, removing it and all related code.
...
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Reviewed-by: Baoquan He <bhe@...hat.com>
> ---
>  include/linux/swap.h       |   3 -
>  include/linux/swap_slots.h |  28 ----
>  mm/Makefile                |   2 +-
>  mm/swap_slots.c            | 295 -------------------------------------
>  mm/swap_state.c            |   8 +-
>  mm/swapfile.c              | 194 ++++++++----------------
>  6 files changed, 67 insertions(+), 463 deletions(-)
>  delete mode 100644 include/linux/swap_slots.h
>  delete mode 100644 mm/swap_slots.c
...
> diff --git a/mm/swapfile.c b/mm/swapfile.c
...
> +swp_entry_t folio_alloc_swap(struct folio *folio)
>  {
> -	int order = swap_entry_order(entry_order);
> -	unsigned long size = 1 << order;
> +	unsigned int order = folio_order(folio);
> +	unsigned int size = 1 << order;
>  	struct swap_info_struct *si, *next;
> -	int n_ret = 0;
> +	swp_entry_t entry = {};
> +	unsigned long offset;
>  	int node;
>  
> +	if (order) {
> +		/*
> +		 * Should not even be attempting large allocations when huge
> +		 * page swap is disabled. Warn and fail the allocation.
> +		 */
> +		if (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER) {
> +			VM_WARN_ON_ONCE(1);
> +			return entry;
> +		}
> +	}

This warning triggers on s390. CONFIG_THP_SWAP is disabled and order
is 8 when this triggers (reproduced with ltp's swapon01 test case):

------------[ cut here ]------------
WARNING: CPU: 1 PID: 895 at mm/swapfile.c:1227 folio_alloc_swap+0x438/0x440
Modules linked in:
CPU: 1 UID: 0 PID: 895 Comm: swapon01 Not tainted 6.14.0-rc6-00227-g0ff67f990bd4-dirty #25
Hardware name: IBM 3931 A01 704 (z/VM 7.4.0)
Krnl PSW : 0704d00180000000 000003ffe051210c (folio_alloc_swap+0x43c/0x440)
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3
Krnl GPRS: 0000000080000000 0000000000000001 0000000000000013 0000000000070000
           0000000000000006 fffffef40e9da000 0000000000000000 0000037202fc4000
           0000037f00000100 0000000000000100 0000037fe2e4b770 0000037202fc4000
           0000000000000000 0000000000000000 000003ffe0512108 0000037fe2e4b3c8
Krnl Code: 000003ffe05120fe: b9160044            llgfr   %r4,%r4
           000003ffe0512102: c0e5ffdf8c0b        brasl   %r14,000003ffe0103918
          #000003ffe0512108: af000000            mc      0,0
          >000003ffe051210c: a7f4fe94            brc     15,000003ffe0511e34
           000003ffe0512110: c0040069ce74        brcl    0,000003ffe124bdf8
           000003ffe0512116: eb8ff0580024        stmg    %r8,%r15,88(%r15)
           000003ffe051211c: b90400ef            lgr     %r14,%r15
           000003ffe0512120: e3f0ffb8ff71        lay     %r15,-72(%r15)
Call Trace:
 [<000003ffe051210c>] folio_alloc_swap+0x43c/0x440 
 [<000003ffe050afa6>] add_to_swap+0x56/0xf0 
 [<000003ffe045fdc0>] shrink_folio_list+0xe80/0x13b0 
 [<000003ffe0461946>] shrink_inactive_list+0x1a6/0x550 
 [<000003ffe04624a2>] shrink_lruvec+0x2b2/0x410 
 [<000003ffe0462840>] shrink_node_memcgs+0x240/0x2d0 
 [<000003ffe0462986>] shrink_node+0xb6/0x3e0 
 [<000003ffe046302a>] do_try_to_free_pages+0xda/0x610 
 [<000003ffe0464d2c>] try_to_free_mem_cgroup_pages+0x14c/0x2a0 
 [<000003ffe0568270>] try_charge_memcg+0x220/0x5d0 
 [<000003ffe056867a>] charge_memcg+0x5a/0x270 
 [<000003ffe056a484>] __mem_cgroup_charge+0x44/0x80 
 [<000003ffe04acf20>] alloc_anon_folio+0x280/0x610 
 [<000003ffe04ad45a>] do_anonymous_page+0x1aa/0x5e0 
 [<000003ffe04af4c4>] __handle_mm_fault+0x244/0x500 
 [<000003ffe04af820>] handle_mm_fault+0xa0/0x170 
 [<000003ffe01533f8>] do_exception+0x1d8/0x4a0 
 [<000003ffe11fb92a>] __do_pgm_check+0x13a/0x220 
 [<000003ffe120c3ce>] pgm_check_handler+0x11e/0x170 
---[ end trace 0000000000000000 ]---