linux-kernel - Re: [PATCH 1/4] mm/filemap: Make MAX_PAGECACHE

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Date: Tue, 25 Jun 2024 20:43:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 djwong@...nel.org, willy@...radead.org, akpm@...ux-foundation.org,
 hughd@...gle.com, torvalds@...ux-foundation.org, zhenyzha@...hat.com,
 shan.gavin@...il.com
Subject: Re: [PATCH 1/4] mm/filemap: Make MAX_PAGECACHE_ORDER acceptable to
 xarray

On 25.06.24 11:06, Gavin Shan wrote:
> The largest page cache order can be HPAGE_PMD_ORDER (13) on ARM64
> with 64KB base page size. The xarray entry with this order can't
> be split as the following error messages indicate.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 35 PID: 7484 at lib/xarray.c:1025 xas_split_alloc+0xf8/0x128
> Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib  \
> nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct    \
> nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4    \
> ip_set rfkill nf_tables nfnetlink vfat fat virtio_balloon drm      \
> fuse xfs libcrc32c crct10dif_ce ghash_ce sha2_ce sha256_arm64      \
> sha1_ce virtio_net net_failover virtio_console virtio_blk failover \
> dimlib virtio_mmio
> CPU: 35 PID: 7484 Comm: test Kdump: loaded Tainted: G W 6.10.0-rc5-gavin+ #9
> Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20240524-1.el9 05/24/2024
> pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> pc : xas_split_alloc+0xf8/0x128
> lr : split_huge_page_to_list_to_order+0x1c4/0x720
> sp : ffff800087a4f6c0
> x29: ffff800087a4f6c0 x28: ffff800087a4f720 x27: 000000001fffffff
> x26: 0000000000000c40 x25: 000000000000000d x24: ffff00010625b858
> x23: ffff800087a4f720 x22: ffffffdfc0780000 x21: 0000000000000000
> x20: 0000000000000000 x19: ffffffdfc0780000 x18: 000000001ff40000
> x17: 00000000ffffffff x16: 0000018000000000 x15: 51ec004000000000
> x14: 0000e00000000000 x13: 0000000000002000 x12: 0000000000000020
> x11: 51ec000000000000 x10: 51ece1c0ffff8000 x9 : ffffbeb961a44d28
> x8 : 0000000000000003 x7 : ffffffdfc0456420 x6 : ffff0000e1aa6eb8
> x5 : 20bf08b4fe778fca x4 : ffffffdfc0456420 x3 : 0000000000000c40
> x2 : 000000000000000d x1 : 000000000000000c x0 : 0000000000000000
> Call trace:
>   xas_split_alloc+0xf8/0x128
>   split_huge_page_to_list_to_order+0x1c4/0x720
>   truncate_inode_partial_folio+0xdc/0x160
>   truncate_inode_pages_range+0x1b4/0x4a8
>   truncate_pagecache_range+0x84/0xa0
>   xfs_flush_unmap_range+0x70/0x90 [xfs]
>   xfs_file_fallocate+0xfc/0x4d8 [xfs]
>   vfs_fallocate+0x124/0x2e8
>   ksys_fallocate+0x4c/0xa0
>   __arm64_sys_fallocate+0x24/0x38
>   invoke_syscall.constprop.0+0x7c/0xd8
>   do_el0_svc+0xb4/0xd0
>   el0_svc+0x44/0x1d8
>   el0t_64_sync_handler+0x134/0x150
>   el0t_64_sync+0x17c/0x180
> 
> Fix it by decreasing MAX_PAGECACHE_ORDER to the largest supported order
> by xarray. For this specific case, MAX_PAGECACHE_ORDER is dropped from
> 13 to 11 when CONFIG_BASE_SMALL is disabled.
> 
> Fixes: 4f6617011910 ("filemap: Allow __filemap_get_folio to allocate large folios")
> Cc: stable@...nel.org # v6.6+
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   include/linux/pagemap.h | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 59f1df0cde5a..a0a026d2d244 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -354,11 +354,18 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
>    * a good order (that's 1MB if you're using 4kB pages)
>    */
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -#define MAX_PAGECACHE_ORDER	HPAGE_PMD_ORDER
> +#define PREFERRED_MAX_PAGECACHE_ORDER	HPAGE_PMD_ORDER
>   #else
> -#define MAX_PAGECACHE_ORDER	8
> +#define PREFERRED_MAX_PAGECACHE_ORDER	8
>   #endif
>   
> +/*
> + * xas_split_alloc() does not support arbitrary orders. This implies no
> + * 512MB THP on ARM64 with 64KB base page size.
> + */
> +#define MAX_XAS_ORDER		(XA_CHUNK_SHIFT * 2 - 1)
> +#define MAX_PAGECACHE_ORDER	min(MAX_XAS_ORDER, PREFERRED_MAX_PAGECACHE_ORDER)
> +
>   /**
>    * mapping_set_large_folios() - Indicate the file supports large folios.
>    * @mapping: The file.

Thanks!

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb