Re: [BK PATCH 2.5] Introduce 64-bit versions of PAGE_{CACHE_,}{MASK,ALIGN}

[William Lee Irwin III <wli@holomorphy.com>]

William Lee Irwin III wrote:
>> Do you know an approximate reasonable constant of proportionality
>> for how many pages have ->private attached?

On Sun, Jul 28, 2002 at 06:36:20PM -0700, Andrew Morton wrote:
> Well, it depends on what the mapping is using ->private for.
> In the case of ext2, ext3 and (soon) reiserfs mappings, ->private
> is only used for pagecache pages which were written to with write(2).
> But for other filesystems, basically all pagecache pages have
> buffers at present, so I exaggerate.  But as filesystems migrate
> to using direct-to-BIO reads, the situation gets better.
> It might be useful to buffer-strip written-to pages as well, if
> a clean way of doing that presents itself.  Maybe in refill_inactive
> or something.

Collecting some numbers might be useful here.


On Sun, Jul 28, 2002 at 05:10:48PM -0700, Andrew Morton wrote:
>>> - Remove the rmap chain (I just broke ptep_to_address() anyway).  4 bytes
>>>   saved.  struct page is now 20 bytes.

William Lee Irwin III wrote:
>> How did ptep_to_address() break? I browsed over your latest changes and
>> missed the bit where that fell apart. I'll at least take a stab at fixing
>> it up until the other bits materialize.

On Sun, Jul 28, 2002 at 06:36:20PM -0700, Andrew Morton wrote:
> I broke it in my five-minute thought-coding exercise.  By removing
> page->index.

Sorry, I took fixing up the users as part of the ->index removal. This
isn't a serious issue.


Cheers,
Bill