Re: [PATCH 2/4] mm: support nesting memalloc_use_memcg()

Roman Gushchin
2020-08-24T16:26:42Z

On Mon, Aug 24, 2020 at 11:36:00AM -0400, Dan Schatzberg wrote:
> From: Johannes Weiner <hannes@cmpxchg.org>
>
> 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: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Roman Gushchin <guro@fb.com>
> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>

Hi Dan,

JFYI: I need a similar patch for the bpf memory accounting rework,
so I ended up sending it separately (with some modifications including
different naming): https://lkml.org/lkml/2020/8/21/1464 .

Can you please, rebase your patchset using this patch?

I hope Andrew can pull this standalone patch into 5.9-rc*,
as Shakeel suggested. It will help us to avoid merge conflicts
during the 5.10 merge window.

Thanks!