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Date:   Wed, 19 Jul 2023 17:00:11 -0700
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, willy@infradead.org,
        songmuchun@bytedance.com, david@redhat.com
Subject: Re: [PATCH v2 0/1] change ->index to PAGE_SIZE for hugetlb pages
Message-ID: <20230720000011.GD3240@monkey>
References: <20230710230450.110064-1-sidhartha.kumar@oracle.com>
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On 07/10/23 16:04, Sidhartha Kumar wrote:
> ========================== OVERVIEW ========================================
> This patchset attempts to implement a listed filemap TODO which is
> changing hugetlb folios to have ->index in PAGE_SIZE. This simplifies many
> functions within filemap.c as they have to special case hugetlb pages.
> From the RFC v1[1], Mike pointed out that hugetlb will still have to maintain
> a huge page sized index as it is used for the reservation map and the hash
> function for the hugetlb mutex table.
> 
> This patchset adds new wrappers for hugetlb code to to interact with the
> page cache. These wrappers calculate a linear page index as this is now
> what the page cache expects for hugetlb pages.
> 
> From the discussion on HGM for hugetlb[3], there is a want to remove hugetlb
> special casing throughout the core mm code. This series accomplishes
> a part of this by shifting complexity from filemap.c to hugetlb.c. There
> are still checks for hugetlb within the filemap code as cgroup accounting
> and hugetlb accounting are special cased as well. 
> 
> =========================== PERFORMANCE =====================================

Hi Sid,

Sorry for being dense but can you tell me what the below performance
information means.  My concern with such a change would be any noticeable
difference in populating a large (up to TB) hugetlb file.  My guess is
that it is going to take longer unless xarray is optimized for this.

We do have users that create and pre-populate hugetlb files this big.
Just want to make sure there are no surprises for them.
-- 
Mike Kravetz


> 6.4.0-rc5
> @hugetlb_add_to_page_cache:                                                                                                                                                                                                     
> [512, 1K)           7518 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|                                                                                                                                   
> [1K, 2K)             158 |@                                                   |                                                                                                                                   
> [2K, 4K)              30 |                                                    |                                                                                                                                   
> [4K, 8K)               6 |                                                    |                                                                                                                                   
> [8K, 16K)              9 |                                                    
> 
> 6.5.0-rc1 + this patch series
> @hugetlb_add_to_page_cache:                                                                                                                                                                                                     
> [512, 1K)           6345 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|                                                                                                                                   
> [1K, 2K)            1308 |@@@@@@@@@@                                          |                                                                                                                                   
> [2K, 4K)              39 |                                                    |                                                                                                                                   
> [4K, 8K)              20 |                                                    |                                                                                                                                   
> [8K, 16K)              8 |                                                    |                                                                                                                                   
> [16K, 32K)             1 |                                                    |  
> 
> 6.4.0-rc5
> @__filemap_get_folio:                                                                                                                                                                                                    
> [256, 512)         11292 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|                                                                                                                                   
> [512, 1K)           4615 |@@@@@@@@@@@@@@@@@@@@@                               |                                                                                                                                   
> [1K, 2K)             960 |@@@@                                                |                                                                                                                                   
> [2K, 4K)             188 |                                                    |                                                                                                                                   
> [4K, 8K)              68 |                                                    |                                                                                                                                   
> [8K, 16K)             14 |                                                    |                                                                                                                                   
> [16K, 32K)             4 |                                                    |                                                                                                                                                                                                                                                                
> [2G, 4G)               4 |                                                    |
> 
> 6.5.0-rc1 + this patch series
> @__filemap_get_folio:    
> @get_folio_ns:                                                                                                                                                                                                    
> [128, 256)            13 |                                                    |                                                                                                                                   
> [256, 512)         11131 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [512, 1K)           5544 |@@@@@@@@@@@@@@@@@@@@@@@@@                           |
> [1K, 2K)             996 |@@@@                                                |
> [2K, 4K)             317 |@                                                   |
> [4K, 8K)              76 |                                                    |
> [8K, 16K)             23 |                                                    |
> [16K, 32K)             6 |                                                    |
> [32K, 64K)             1 |                                                    |
> [64K, 128K)            0 |                                                    |
> [128K, 256K)           0 |                                                    |
> [256K, 512K)           0 |                                                    |
> [512K, 1M)             0 |                                                    |
> [1M, 2M)               0 |                                                    |
> [2M, 4M)               0 |                                                    |
> [4M, 8M)               0 |                                                    |
> [8M, 16M)              0 |                                                    |
> [16M, 32M)             0 |                                                    |
> [32M, 64M)             0 |                                                    |
> [64M, 128M)            0 |                                                    |
> [128M, 256M)           0 |                                                    |
> [256M, 512M)           0 |                                                    |
> [512M, 1G)             0 |                                                    |
> [1G, 2G)               0 |                                                    |
> [2G, 4G)               3 |                                                    
> 
> =========================== TESTING ==========================================
> This series passes the LTP hugetlb test cases as well as the libhugetlbfs tests.
> 
> ********** TEST SUMMARY
> *                      2M            
> *                      32-bit 64-bit 
> *     Total testcases:   110    113   
> *             Skipped:     0      0   
> *                PASS:   107    113   
> *                FAIL:     0      0   
> *    Killed by signal:     3      0   
> *   Bad configuration:     0      0   
> *       Expected FAIL:     0      0   
> *     Unexpected PASS:     0      0   
> *    Test not present:     0      0   
> * Strange test result:     0      0   
> **********
> 
> 
> 
> RFC v2[2]-> v1:
>   -cleanup code style
> 
> RFC v1 -> v2
>   -change direction of series to maintain both huge and base page size index
>    rather than try to get rid of all references to a huge page sized index.
> 
> v1 -> v2
>   - squash seperate filemap and hugetlb patches into one to allow for bisection
>     per Matthew
>   - get rid of page_to_index()
>   - fix errors in hugetlb_fallocate() and remove_inode_hugepages()
> 
> 
> rebased on 07/10/2023 mm-unstable
> 
> 
> Sidhartha Kumar (1):
>   mm/filemap: remove hugetlb special casing in filemap.c
> 
>  fs/hugetlbfs/inode.c    | 10 +++++-----
>  include/linux/hugetlb.h | 12 ++++++++++++
>  include/linux/pagemap.h | 26 ++------------------------
>  mm/filemap.c            | 36 +++++++++++-------------------------
>  mm/hugetlb.c            | 11 ++++++-----
>  5 files changed, 36 insertions(+), 59 deletions(-)
> 
> -- 
> 2.41.0
>