Re: Re: Windows OpCache bug fix

On Mon, Oct 5, 2015 at 3:51 PM, Anatol Belski <anatol.php@belski.net> wrote: > > > > -----Original Message----- > > From: Dmitry Stogov [mailto:dmitry@zend.com] > > Sent: Monday, October 5, 2015 1:08 PM > > To: Anatol Belski <anatol.php@belski.net> > > Cc: Matt Ficken <themattficken@gmail.com>; Pierre Joye > > <pierre.php@gmail.com>; Laruence <laruence@php.net>; PHP Internals > > <internals@lists.php.net>; dmitry@php.net > > Subject: Re: [PHP-DEV] Re: Windows OpCache bug fix > > > > On Mon, Oct 5, 2015 at 10:29 AM, Anatol Belski <anatol.php@belski.net> > > wrote: > > > > > Hi Dmitry, > > > > > > > -----Original Message----- > > > > From: Dmitry Stogov [mailto:dmitry@zend.com] > > > > Sent: Friday, October 2, 2015 9:34 AM > > > > To: Anatol Belski <anatol.php@belski.net> > > > > Cc: Matt Ficken <themattficken@gmail.com>; Pierre Joye > > > > <pierre.php@gmail.com>; Anatoliy Belsky <ab@php.net>; Laruence > > > > <laruence@php.net>; PHP Internals <internals@lists.php.net>; > > > dmitry@php.net > > > > Subject: Re: [PHP-DEV] Re: Windows OpCache bug fix > > > > > > > > > Dmitry, I'd have a question to this > > > > > > Also. if we can't map SHM into desired address space, we may map > > > > > > it in > > > > > any > > > > > > other address and copy data into the process memory similar to > > > > > file-cache. > > > > > In randomized memory layout, even the base were available and > > > > > OpenFileMapping were worky, some parts of that memory were already > > > > taken. > > > > > How exactly it could be done, could you please give a couple of > > > > > pointers to this? > > > > > > > > > > > > If MapViewOfFileEx(..., wanted_mapping_base) fails, we do > > > > MapViewOfFileEx(..., NULL). > > > > > > > > > > > > > Would the file cache be always required then? > > > > > > > > > > > > > This is not necessary, but depends on implementation of course. > > > > > > > Thanks for the advice. I was playing with this over these days. There > > > are two usual cases where it possibly fails when reattaching ATM > > > > > > - > > > > > > https://github.com/php/php-src/blob/PHP-7.0/ext/opcache/shared_alloc_w > > > in32.c#L151 > > > - the saved address is available but is not suitable > > > - > > > > > > https://github.com/php/php-src/blob/PHP-7.0/ext/opcache/shared_alloc_w > > > in32.c#L159 > > > - the actual MapViewOfFileEx case > > > > > > An unrelated plain C test shows, that MapViewOfFileEx can possibly > > > fail when called second time, too. Even with NULL or with another > > > address as base. But even if it could map at a different base - the > > > internal structures will probably have invalid addresses. > > > > > > right. we might need different code for zend_accle_hash access or convert > > corresponding structures to PIC. > > For opcdeos "invalid address" don't matter because we will copy them into > > process memory and fix (like in file-cache). > > > Ah, I have to study the file cache code then. But generally it sounds not > like something that can be done offhand. I've also thought about other > things like interned strings (maybe something else), not sure they're > stored with the cache. > > > > > > So it looks like there's indeed no profit to do any retry once the > > > actualy base address needed was failed to reattach to. > > > > > > IMHO the scenario that were usable - in case it fails to reattach to > > > the exact address, it has to switch to heap. Just for one request, it > > > should get a heap allocated segment and then invalidate all the cache. > > > That way we fulfill the following > > > > > > - the request is served for sure > > > - the scripts are not cached indeed, so no divergence with the actual > > > real cache > > > > > > A heap fallback memory handler would be probably quite easy to > implement. > > > What do you think? > > > > > > Apropos with the heap - it also looks like when PHP is used as module > > > under mpm_winnt, all the cache could use heap instead of SHM. In that > > > case, there is only one Apache process serving with many threads. > > > Except one would want to share that cache outside Apache, using heap > > > there could be a much simpler solution. > > > > > > > Heap based cache makes the same problems. It increase the memory usage > and > > doesn't provide cache consistency. > > Just fall-back to file-cache may be better. > Do you think something like this would suffice as file cache fallback > https://gist.github.com/weltling/224001a468f04de13693 ? Though > it'd > still diverge from the "main" cache. > I think we should enable file-cache automatically, but we can set ZCG(accel_directives).file_cache_only if the file_cache already enabled. > > Actually in such case all the processes should switch to file cache? No. Only the processes that weren't be able to attach to SHM. > Just not sure how they all would negotiate that when no SHM is available > (probably through files, or a separate shared chunk). > yeah. Processes that use file-cache-only won't be able to negotiate SHM cache. :( > > > > > Actually, when I implemented file-cache I had a though about different > storage > > back-ends (e.g. sqlite or memcache). > > This abstraction might make support for "improperly mapped SHM" quite > easy. > > > Yeah, that could be useful. Maybe also module based so one could even > supply them separately, then an arbitrary storage mechanism could be > provided. Fe like I've mentioned for mpm_winnt -if there's no intention to > share the cache outside Apache, just one heap for all could be much simpler > to avoid all that reattach mechanics. > Does mpm_winnt use pure ZTS without processes? Thanks. Dmitry. > > Thanks. > > Anatol > >