linux-kernel - Re: [PATCH v3 00/25] Large pages in the page cache

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Date:   Wed, 29 Apr 2020 18:40:02 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/25] Large pages in the page cache

On Wed, Apr 29, 2020 at 06:36:32AM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> This patch set does not pass xfstests.  Test at your own risk.  It is
> based on the readahead rewrite which is in Andrew's tree.  The large
> pages somehow manage to fall off the LRU, so the test VM quickly runs
> out of memory and freezes.  To reproduce:
> 
> # mkfs.xfs /dev/sdb && mount /dev/sdb /mnt && dd if=/dev/zero bs=1M count=2048 of=/mnt/bigfile && sync && sleep 2 && sync && echo 1 >/proc/sys/vm/drop_caches 
> # /host/home/willy/kernel/xarray-2/tools/vm/page-types | grep thp
> 0x0000000000401800	       511        1  ___________Ma_________t____________________	mmap,anonymous,thp
> 0x0000000000405868	         1        0  ___U_lA____Ma_b_______t____________________	uptodate,lru,active,mmap,anonymous,swapbacked,thp
> # dd if=/mnt/bigfile of=/dev/null bs=2M count=5
> # /host/home/willy/kernel/xarray-2/tools/vm/page-types | grep thp
> 0x0000000000400000	      2516        9  ______________________t____________________	thp
> 0x0000000000400028	         1        0  ___U_l________________t____________________	uptodate,lru,thp
> 0x000000000040006c	       106        0  __RU_lA_______________t____________________	referenced,uptodate,lru,active,thp

Note that you have 107 pages on LRU. It is only head pages. With order-5
pages it is over 13MiB.

Looks like everything is fine.

> 0x0000000000400228	         1        0  ___U_l___I____________t____________________	uptodate,lru,reclaim,thp
> 0x0000000000401800	       511        1  ___________Ma_________t____________________	mmap,anonymous,thp
> 0x0000000000405868	         1        0  ___U_lA____Ma_b_______t____________________	uptodate,lru,active,mmap,anonymous,swapbacked,thp
> 
> 
> The principal idea here is that a large part of the overhead in dealing
> with individual pages is that there's just so darned many of them.  We
> would be better off dealing with fewer, larger pages, even if they don't
> get to be the size necessary for the CPU to use a larger TLB entry.
> 
> Matthew Wilcox (Oracle) (24):
>   mm: Allow hpages to be arbitrary order
>   mm: Introduce thp_size
>   mm: Introduce thp_order
>   mm: Introduce offset_in_thp
>   fs: Add a filesystem flag for large pages
>   fs: Introduce i_blocks_per_page
>   fs: Make page_mkwrite_check_truncate thp-aware
>   fs: Support THPs in zero_user_segments
>   bio: Add bio_for_each_thp_segment_all
>   iomap: Support arbitrarily many blocks per page
>   iomap: Support large pages in iomap_adjust_read_range
>   iomap: Support large pages in read paths
>   iomap: Support large pages in write paths
>   iomap: Inline data shouldn't see large pages
>   xfs: Support large pages
>   mm: Make prep_transhuge_page return its argument
>   mm: Add __page_cache_alloc_order
>   mm: Allow large pages to be added to the page cache
>   mm: Allow large pages to be removed from the page cache
>   mm: Remove page fault assumption of compound page size
>   mm: Add DEFINE_READAHEAD
>   mm: Make page_cache_readahead_unbounded take a readahead_control
>   mm: Make __do_page_cache_readahead take a readahead_control
>   mm: Add large page readahead
> 
> William Kucharski (1):
>   mm: Align THP mappings for non-DAX
> 
>  drivers/nvdimm/btt.c    |   4 +-
>  drivers/nvdimm/pmem.c   |   6 +-
>  fs/ext4/verity.c        |   4 +-
>  fs/f2fs/verity.c        |   4 +-
>  fs/iomap/buffered-io.c  | 110 ++++++++++++++++--------------
>  fs/jfs/jfs_metapage.c   |   2 +-
>  fs/xfs/xfs_aops.c       |   4 +-
>  fs/xfs/xfs_super.c      |   2 +-
>  include/linux/bio.h     |  13 ++++
>  include/linux/bvec.h    |  23 +++++++
>  include/linux/fs.h      |   1 +
>  include/linux/highmem.h |  15 +++--
>  include/linux/huge_mm.h |  25 +++++--
>  include/linux/mm.h      |  97 ++++++++++++++-------------
>  include/linux/pagemap.h |  62 ++++++++++++++---
>  mm/filemap.c            |  60 ++++++++++++-----
>  mm/highmem.c            |  62 ++++++++++++++++-
>  mm/huge_memory.c        |  49 ++++++--------
>  mm/internal.h           |  13 ++--
>  mm/memory.c             |   7 +-
>  mm/page_io.c            |   2 +-
>  mm/page_vma_mapped.c    |   4 +-
>  mm/readahead.c          | 145 ++++++++++++++++++++++++++++++----------
>  23 files changed, 485 insertions(+), 229 deletions(-)
> 
> -- 
> 2.26.2
> 

-- 
 Kirill A. Shutemov