[llvm] r329648 - [CachePruning] Fix comment about ext4 per-directory file limit. NFC
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 10 10:35:57 PDT 2018
On 2018-04-09, Peter Collingbourne wrote:
>Are you sure about that? I'm pretty sure that before writing that comment I
>wrote a small program that created lots of files (not subdirectories) in a
>directory until it started getting error messages, which started happening at
>around 6000000 files.
>
>Peter
I guess you created a file of 100GiB. The number of inodes is roughly 6553600.
100*1024*1024*1024 / 16384 = 6553600.0 where 16384 is the default bytes-per-inode (man mke2fs).
% truncate -s 100G 100G
% mkfs.ext4 100G
% dumpe2fs 100G
.....
Inode count: 6553600
.....
Each file consumes one inode and the number of files in that directory
is limited by this factor.
>
>On Mon, Apr 9, 2018 at 5:12 PM, Fangrui Song via llvm-commits <
>llvm-commits at lists.llvm.org> wrote:
>
> Author: maskray
> Date: Mon Apr 9 17:12:28 2018
> New Revision: 329648
>
> URL: http://llvm.org/viewvc/llvm-project?rev=329648&view=rev
> Log:
> [CachePruning] Fix comment about ext4 per-directory file limit. NFC
>
> There is a limit on number of subdirectories if dir_nlinks is not
> enabled (31998), but per-directory number of files is not limited.
>
> Modified:
> llvm/trunk/include/llvm/Support/CachePruning.h
>
> Modified: llvm/trunk/include/llvm/Support/CachePruning.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/
> CachePruning.h?rev=329648&r1=329647&r2=329648&view=diff
> ===========================================================================
> ===
> --- llvm/trunk/include/llvm/Support/CachePruning.h (original)
> +++ llvm/trunk/include/llvm/Support/CachePruning.h Mon Apr 9 17:12:28 2018
> @@ -52,9 +52,8 @@ struct CachePruningPolicy {
> /// the number of files based pruning.
> ///
> /// This defaults to 1000000 because with that many files there are
> - /// diminishing returns on the effectiveness of the cache, and some file
> - /// systems have a limit on how many files can be contained in a
> directory
> - /// (notably ext4, which is limited to around 6000000 files).
> + /// diminishing returns on the effectiveness of the cache, and file
> + /// systems have a limit on total number of files.
> uint64_t MaxSizeFiles = 1000000;
> };
>
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>--
>--
>Peter
--
宋方睿
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