On Wed, 2013-09-11 at 21:21 +0200, Lukas Slebodnik wrote:
On (11/09/13 12:50), Simo Sorce wrote:
>On Wed, 2013-09-11 at 17:39 +0200, Lukas Slebodnik wrote:
>> On (11/09/13 16:30), Michal Židek wrote:
>> >On 09/11/2013 04:16 PM, Simo Sorce wrote:
>> >>On Wed, 2013-09-11 at 15:58 +0200, Lukas Slebodnik wrote:
>> >>>On (11/09/13 09:39), Simo Sorce wrote:
>> >>>>On Wed, 2013-09-11 at 12:24 +0200, Lukas Slebodnik wrote:
>> >>>>>ehlo,
>> >>>>>
>> >>>>>Two patches are attached.
>> >>>>>
>> >>>>>The 1st patch reverts commit
4662725ffef62b3b2502481438effa7c8fef9f80.
>> >>>>>"mmap_cache: Skip records which doesn't have same
hash"
>> >>>>> --next patch lokks nicer with recerted commit 4662725ffe
>> >>>>>
>> >>>>>
>> >>>>>The 2nd patch changes behaviour of record chaining.
>> >>>>>
>> >>>>>LS
>> >>>>
>> >>>>NACK, you cannot just change the record structure w/o bumping
the whole
>> >>>>mmap MAJOR version number.
>> >>>>
>> >>>>Aside:
>> >>>>
>> >>>>If we are not I am thinking whether we should do some other
>> >>>>optimizations to keep the size down.
>> >>>>
>> >>>>For example, hashes are generally relatively small quantities as
we do
>> >>>>not allow huge tables. If we can limit tables size to a max of
65k
>> >>>>elements we could change the hash type from uint32_t to
uint16_t, and
>> >>>>end up using the same size we are using now.
>> >>>>We already limit the total mmap size to 4G as rel_prt_t is a
uint32_t,
>> >>>>and in practice we'll never allow maps with a very large
size as it eats
>> >>>>into the memory available to 32 bit processes.
>> >>>>So perhaps 65k for the hash tables is an acceptable limit. (I
think we
>> >>>>currently have a 100k limit which is probably a little bit
overblown as
>> >>>>a default anyway.
>> >>>>
>> >>>>Simo.
>> >>>>
>> >>>I would rather reduce "uint64_t expire" into
"uint32_t expire_offset"
>> >>>
>> >>>expire_offset will be time since creation of mmap cache.
>> >>>and uint64_t "creation_time" will be stored in
"struct sss_mc_ctx"
>> >>
>> >>Uhmm, I do agree that 4billion seconds offset is probably ok, but then
>> >>it means the information is split in 2 different places, and this will
>> >>make clients more complicated, as clients will have to keep track of
the
>> >>creation time + expiration offset now ...
>> >>
>> >>>Do you agree?
>> >>
>> >>I am not 100% convinced yet, although I do agree that it would save
>> >>quite some space.
>> >>
>> >>>Do I need to increment SSS_MC_MAJOR_VNO or only SSS_MC_MINOR_VNO?
>> >>
>> >>Major, you are completely changing the structure, an older client
cannot
>> >>be allowed to use the new map unless it explicitly know the layout
>> >>changed.
>> >
>> >Well, if we already have to change the major version, I would go with
>> >the two 32 bit next1 and nex2 members. If we really want to keep the
>> >current size of the record (btw. why? We have to change the major ver.
>> >anyway) then I like the two 16 bit pointers next1 and next2 more than
>> >the 32 bit time offset (the memcache is just another cache layer, so it
>> >does not have to be "gigantic"... 16 bit pointers are just fine
IMO).
>> >
>> I don't like 16 bit next pointers.
>>
>> Default value of hash table size is 100000 (for passwd)
>> It is 53% greater value than UINT_16_MAX.
>> If we decided to enlarge this default value in future, we would be still
>> limited by UINT_16_MAX.
>>
>> I think it is not good idea to reduce size of next pointers.
>
>I am thinking we might want to change the way we create the way we
>handle record size to see if we can make a change that will be more
>future proof.
>
>If we stored the size of the records in the header and always calculate
>the position of b2 based on that information then we could introduce a
>variable size record structure. This would allow in future to increase
>the size of the structure for optional parameters w/o necessarily having
>to bump up the major version.
>
>However I want to have at the very least 64bit alignemtn always
>preserverd, so from 32 bytes we want to grow in 8 bytes steps, which
>means adding a uint32_t padding before b2.
totally agree.
SSS_MC_MAJOR_VNO was increased.
padding was added. sizeof(struct sss_mc_ctx) will be 40
Updated patches are attached.
It looks ok to me.
However, just to be clear we are planning on pushing this to 1.12 only
right ?
I am not hugely comfortable with pushing it to existing releases.
Simo.
--
Simo Sorce * Red Hat, Inc * New York