> -----Original Message----- > From: Dmitry Stogov [mailto:dmi...@zend.com] > Sent: Monday, October 5, 2015 1:08 PM > To: Anatol Belski <anatol....@belski.net> > Cc: Matt Ficken <themattfic...@gmail.com>; Pierre Joye > <pierre....@gmail.com>; Laruence <larue...@php.net>; PHP Internals > <internals@lists.php.net>; dmi...@php.net > Subject: Re: [PHP-DEV] Re: Windows OpCache bug fix > > On Mon, Oct 5, 2015 at 10:29 AM, Anatol Belski <anatol....@belski.net> > wrote: > > > Hi Dmitry, > > > > > -----Original Message----- > > > From: Dmitry Stogov [mailto:dmi...@zend.com] > > > Sent: Friday, October 2, 2015 9:34 AM > > > To: Anatol Belski <anatol....@belski.net> > > > Cc: Matt Ficken <themattfic...@gmail.com>; Pierre Joye > > > <pierre....@gmail.com>; Anatoliy Belsky <a...@php.net>; Laruence > > > <larue...@php.net>; PHP Internals <internals@lists.php.net>; > > dmi...@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. Actually in such case all the processes should switch to file cache? Just not sure how they all would negotiate that when no SHM is available (probably through files, or a separate shared chunk). > > 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. Thanks. Anatol -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
