Re: TMPFS Maximum File Size

[Hugh Dickins <hughd@google.com>]

On Wed, Oct 20, 2010 at 6:44 AM, Tharindu Rukshan Bamunuarachchi
<btharindu@gmail.com> wrote:
>
> Is there any kind of file size limitation in TMPFS ?

There is, but it should not be affecting you.  In your x86_64 case,
the tmpfs filesize limit should be slightly over 256GB.

(There's no good reason for that limit when CONFIG_SWAP is not set,
and it's then just a waste of memory on those swap vectors: I've long
wanted to #iifdef CONFIG_SWAP them, but never put in the work to do so
cleanly.)

> Our application SEGFAULT inside write() after filling 70% of TMPFS
> mount. (re-creatable but does not happen every time).

I've no idea why that should be happening: I wonder if your case is
actually triggering some memory corruption, in application or in
kernel, that manifests in that way.

But I don't quite understand what you're seeing either: a segfault in
the write() library call of your libc?  an EFAULT from the kernel's
sys_write()?

Hugh

>
> We are using 98GB TMPFS without swap device. i.e. SWAP is turned off.
> Applications does not take approx. 20GB memory.
>
> we have Physical RAM of 128GB Intel x86 box running SLES 11 64bit.
> We use Infiniband, export TMPFS over NFS and IBM GPFS in same box.
> (hope those won't affect)
>
> Bit confused about "triple-indirect swap vector" ?
>
> Extracted from shmem.c ....
>
> /*
>  * The maximum size of a shmem/tmpfs file is limited by the maximum size of
>  * its triple-indirect swap vector - see illustration at shmem_swp_entry().
>  *
>  * With 4kB page size, maximum file size is just over 2TB on a 32-bit kernel,
>  * but one eighth of that on a 64-bit kernel.  With 8kB page size, maximum
>  * file size is just over 4TB on a 64-bit kernel, but 16TB on a 32-bit kernel,
>  * MAX_LFS_FILESIZE being then more restrictive than swap vector layout.
>  *
>
> Thankx a lot.
> __
> Tharindu R Bamunuarachchi.
>

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