[llvm] r329648 - [CachePruning] Fix comment about ext4 per-directory file limit. NFC

[Peter Collingbourne via llvm-commits]

No, these were empty files. It wasn't an inode limit because I could still
create files in other directories.

Peter

On Tue, Apr 10, 2018 at 10:35 AM, Fangrui Song <maskray at google.com> wrote:

> 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;
>>     };
>>
>>    _______________________________________________
>>    llvm-commits mailing list
>>    llvm-commits at lists.llvm.org
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>>
>> --
>> --
>> Peter
>>
>
> --
> 宋方睿
>



-- 
-- 
Peter
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