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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 20 Apr 2020 17:43:47 -0700
Message-ID: <CALvZod4GizLVogLoGObxqXveeFX+vBm2SEpHNYA+Yz+Op7o0Qg@mail.gmail.com>
Subject: Re: [PATCH 2/4] mm: support nesting memalloc_use_memcg()
To:     Dan Schatzberg <schatzberg.dan@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Jan Kara <jack@suse.cz>, Amir Goldstein <amir73il@gmail.com>,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>, Roman Gushchin <guro@fb.com>,
        Chris Down <chris@chrisdown.name>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        <linux-fsdevel@vger.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <linux-mm@kvack.org>
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On Mon, Apr 20, 2020 at 3:41 PM Dan Schatzberg <schatzberg.dan@gmail.com> wrote:
>
> The memalloc_use_memcg() function to override the default memcg
> accounting context currently doesn't nest. But the patches to make the
> loop driver cgroup-aware will end up nesting:
>
> [   98.137605]  alloc_page_buffers+0x210/0x288
> [   98.141799]  __getblk_gfp+0x1d4/0x400
> [   98.145475]  ext4_read_block_bitmap_nowait+0x148/0xbc8
> [   98.150628]  ext4_mb_init_cache+0x25c/0x9b0
> [   98.154821]  ext4_mb_init_group+0x270/0x390
> [   98.159014]  ext4_mb_good_group+0x264/0x270
> [   98.163208]  ext4_mb_regular_allocator+0x480/0x798
> [   98.168011]  ext4_mb_new_blocks+0x958/0x10f8
> [   98.172294]  ext4_ext_map_blocks+0xec8/0x1618
> [   98.176660]  ext4_map_blocks+0x1b8/0x8a0
> [   98.180592]  ext4_writepages+0x830/0xf10
> [   98.184523]  do_writepages+0xb4/0x198
> [   98.188195]  __filemap_fdatawrite_range+0x170/0x1c8
> [   98.193086]  filemap_write_and_wait_range+0x40/0xb0
> [   98.197974]  ext4_punch_hole+0x4a4/0x660
> [   98.201907]  ext4_fallocate+0x294/0x1190
> [   98.205839]  loop_process_work+0x690/0x1100
> [   98.210032]  loop_workfn+0x2c/0x110
> [   98.213529]  process_one_work+0x3e0/0x648
> [   98.217546]  worker_thread+0x70/0x670
> [   98.221217]  kthread+0x1b8/0x1c0
> [   98.224452]  ret_from_fork+0x10/0x18
>
> where loop_process_work() sets the memcg override to the memcg that
> submitted the IO request, and alloc_page_buffers() sets the override
> to the memcg that instantiated the cache page, which may differ.
>
> Make memalloc_use_memcg() return the old memcg and convert existing
> users to a stacking model. Delete the unused memalloc_unuse_memcg().
>
> Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>

This patch was from Johannes, so I would suggest to keep his
authorship and signoff along with your signoff.

Reviewed-by: Shakeel Butt <shakeelb@google.com>