Re: (reiserfs) Re: More on Re: (reiserfs) Reiserfs and ext2fs (was Re: (reiserfs) Sum Benchmarks (these look typical?))

[ebiederm+eric@npwt.net (Eric W. Biederman)]

>>>>> "ST" == Stephen C Tweedie <sct@redhat.com> writes:

ST> Hi,
ST> On 30 Jun 1998 19:17:15 -0500, ebiederm+eric@npwt.net (Eric
ST> W. Biederman) said:

>> When either I trace through the code, or a hardware guy convinces me,
>> that it is safe to both write to a page, and do DMA from a page
>> simultaneously I'll believe it.

ST> Read the source code!  We already do this.  If one process or thread
ST> msync()s a mapped file, its dirty pages get written to disk,
ST> independently of any other processes on the same or other CPUs which
ST> may still have the pages mapped and may still be writing to them.  We
ST> don't unmap pages for write; we just mark them non-dirty around all
ST> ptes.

I just took the time and looked.  

And in buffer.c in get_hash_table if we are returning a locked buffer,
we always wait on that buffer until it is unlocked.  So to date we I
don't see us tempting fate, with writing to locked buffers.

It may be harmless but I have't seen that yet.

Eric