Re: tmpfs status

[Maksym Planeta]

Samuel Thibault <samuel.thibault@gnu.org> writes:

> Maksym Planeta, le Sat 07 Apr 2012 23:20:13 +0300, a écrit :
>> > No: as I said, allocate an empty map, so that the existing code can poke
>> > at it without testing for its presence or not.
>> >
>> >> Purpose of this conditions is checking whether map (or submap) is
>> >> already empty.
>> >
>> > Not empty, but allocated.
>> 
>> So, if, for instance, only one page of large object (that needs indirect
>> mapping) was evicted, the whole map would be allocated? And what the
>> purpose of two-level system in this case?
>
> I'm not saying to fill the whole two-level system.
>
> I'm saying to allocate the one-level system when truncation brings from
> two-level to one-level while the first map of the two-level happens to
> be NULL.
>

But thus you will not avoid conditions, because most of them are applied
to second level. Also you will need to allocate memory map for every
object is created even it would not ever use pageout.

>> >> >> > There is also an issue with
>> >> >> >
>> >> >> > +           if (!pager->map) {
>> >> >> > +                invalidate_block (pager_offset);
>> >> >> > +                goto done;
>> >> >> > +            }
>> >> >> >             pager_offset = pager->map[f_page];
>> >> >> >
>> >> >> > at that point, pager_offset is not initialized yet...
>> >> >> >
>> >> >> 
>> >> >> invalidate_block is a macro that sets pager_offset, so, really,
>> >> >> pager_offset shouldn't been initialized yet.
>> >> >
>> >> > It sets the *content* pointed by pager_offset. It does not set the
>> >> > pager_offset pointer.
>> >> 
>> >> pager_offset is not a pointer, it is a union.
>> >
>> > Oops, indeed, sorry about that. I'm still wondering, however: rather
>> > than a goto, why not just putting pager_offset = pager->map[f_page] in
>> > the else part?
>> >
>> 
>> pager_offset = pager->map[f_page] could be just put in else block, but I
>> did so because "goto done" shows clearer that everything was done and
>> execution could be move to finalization part. Just a matter of style. Do
>> you think that this should be changed?
>
> In both cases pager_offset is filled with something, so I don't see why
> it should be different. In the indirect map case, it's a mere else.
>

But pager_offset is filled anyway: either in condition or after.

Regards,
Maksym Planeta.