Re: [PATCH 1/3] Preserve the dirty bit in init_page_buffers

[ebiederm@xmission.com (Eric W. Biederman)]

Nick Piggin <nickpiggin@yahoo.com.au> writes:

> Eric W. Biederman wrote:
>> Nick Piggin <nickpiggin@yahoo.com.au> writes:
>
>>>I would have thought we can fix this simply by removing the
>>>broken ramdisk_set_page_dirty (as far as the comment goes, we
>>>set CAP_NO_ACCT_DIRTY anyway, so the normal set_page_dirty
>>>should handle everything properly, no?).
>>
>>
>> No.  I don't know where accounting comes into play.  I didn't
>> trace that path.  But if we have a non-dirty ramdisk page with
>> buffers (basically a hole in the middle or at the end of the ramdisk).
>> We need to set the buffer dirty bits when we write to it.
>
> Accounting is done in set_page_dirty.

Yes.  What I meant was I had not looked at the implications of
accounting, so I had not looked to see if I could use a generic
set_dirty_page.

I only got as far as recognizing that __set_page_dirty_no_writeback as
not the appropriate function to use because we need to handle buffer
heads.

>> So I don't see how it would make sense to reuse the generic
>> set_page_dirty, and handling all of the logic in set_page_dirty
>> to dirty the buffer heads seemed to have made the most sense.
>
> That's what the generic set_page_dirty does. What I want to know
> is why *doesn't* it make sense to reuse the generic set_page_dirty?
> Unless there is a good reason, then reusing is better than writing
> your own.

I did not look at that part in detail.  I only realized
ramdisk_set_dirty_page needed to be modified upon a final review of my
code, as it was not a case I actually hit.

Just skimming through it again quickly I don't see a reason at this
point to preserve a separate set_dirty_page for the ramdisk code.

Eric