Help with shared memory usage

[Filipe Da Silva]

Hello,,

AFAIK, the patch attached here :
 http://mailman.nginx.org/pipermail/nginx-devel/2013-December/004721.html
compile, and should work on 1.6 too.

Maybe the merge is a bit tricky with the last changes made on ngx_slab.c
I have a up-to-date version on my patch queue.

as Maxim stated, it still needs a functional rework .
http://mailman.nginx.org/pipermail/nginx-devel/2013-October/004337.html

Best,
Filipe

2014-04-25 21:47 GMT+02:00 John Watson <john at disqus.com>:
> Hi Maxim,
>
> Any chance you can fix up this patch and get it into 1.7?
>
> This patch is not compatible with 1.6.
>
> Best,
>
> John
>
> On Wed, Jan 22, 2014 at 8:51 AM, Maxim Dounin <mdounin at mdounin.ru> wrote:
>> Hello!
>>
>> On Wed, Jan 22, 2014 at 01:39:54AM -0200, Wandenberg Peixoto wrote:
>>
>>> Hello Maxim,
>>>
>>> did you have opportunity to take a look on this last patch?
>>
>> It looks more or less correct, though I don't happy with the
>> checks done, and there are various style issues.  I'm planning to
>> look into it and build a better version as time permits.
>>
>>>
>>>
>>> Regards,
>>> Wandenberg
>>>
>>>
>>> On Thu, Dec 26, 2013 at 10:12 PM, Wandenberg Peixoto
>>> <wandenberg at gmail.com>wrote:
>>>
>>> > Hello Maxim,
>>> >
>>> > I changed the patch to check only the p->next pointer.
>>> > And checking if the page is in an address less than the (pool->pages +
>>> > pages).
>>> >
>>> > +    ngx_slab_page_t *prev, *p;
>>> > +    ngx_uint_t        pages;
>>> > +    size_t            size;
>>> > +
>>> > +    size = pool->end - (u_char *) pool - sizeof(ngx_slab_pool_t);
>>> > +    pages = (ngx_uint_t) (size / (ngx_pagesize +
>>> > sizeof(ngx_slab_page_t)));
>>> >  +
>>> > +    p = &page[page->slab];
>>> > +
>>> > +    if ((p < pool->pages + pages) &&
>>> > +            (p->next != NULL) &&
>>> > +            ((p->prev & NGX_SLAB_PAGE_MASK) == NGX_SLAB_PAGE)) {
>>> >
>>> >
>>> > I hope that now I did the right checks.
>>> >
>>> > Regards,
>>> > Wandenberg
>>> >
>>> >
>>> > On Fri, Dec 20, 2013 at 2:49 PM, Maxim Dounin <mdounin at mdounin.ru> wrote:
>>> >
>>> >> Hello!
>>> >>
>>> >> On Tue, Dec 17, 2013 at 09:05:16PM -0200, Wandenberg Peixoto wrote:
>>> >>
>>> >> > Hi Maxim,
>>> >> >
>>> >> > sorry for the long delay. I hope you remember my issue.
>>> >> > In attach is the new patch with the changes you suggest.
>>> >> > Can you check it again? I hope it can be applied to nginx code now.
>>> >> >
>>> >> > About this point "2. There is probably no need to check both prev and
>>> >> > next.",
>>> >> > I check both pointers to avoid a segmentation fault, since in some
>>> >> > situations the next can be NULL and the prev may point to pool->free.
>>> >> > As far as I could follow the code seems to me that could happen one of
>>> >> this
>>> >> > pointers, next or prev, point to a NULL.
>>> >> > I just made a double check to protect.
>>> >>
>>> >> As far as I see, all pages in the pool->free list are expected to
>>> >> have both p->prev and p->next set.  And all pages with type
>>> >> NGX_SLAB_PAGE will be either on the pool->free list, or will have
>>> >> p->next set to NULL.
>>> >>
>>> >> [...]
>>> >>
>>> >> > > > +{
>>> >> > > > +    ngx_slab_page_t *neighbour = &page[page->slab];
>>> >> > >
>>> >> > > Here "neighbour" may point outside of the allocated page
>>> >> > > structures if we are freeing the last page in the pool.
>>> >>
>>> >> It looks like you've tried to address this problem with the
>>> >> following check:
>>> >>
>>> >> > +static ngx_int_t
>>> >> > +ngx_slab_merge_pages(ngx_slab_pool_t *pool, ngx_slab_page_t *page)
>>> >> > +{
>>> >> > +    ngx_slab_page_t *prev, *p;
>>> >> > +
>>> >> > +    p = &page[page->slab];
>>> >> > +    if ((u_char *) p >= pool->end) {
>>> >> > +        return NGX_DECLINED;
>>> >> > +    }
>>> >>
>>> >> This looks wrong, as pool->end points to the end of the pool, not
>>> >> the end of allocated page structures.
>>> >>
>>> >> --
>>> >> Maxim Dounin
>>> >> http://nginx.org/
>>> >>
>>> >> _______________________________________________
>>> >> nginx-devel mailing list
>>> >> nginx-devel at nginx.org
>>> >> http://mailman.nginx.org/mailman/listinfo/nginx-devel
>>> >>
>>> >
>>> >
>>
>>> _______________________________________________
>>> nginx-devel mailing list
>>> nginx-devel at nginx.org
>>> http://mailman.nginx.org/mailman/listinfo/nginx-devel
>>
>>
>> --
>> Maxim Dounin
>> http://nginx.org/
>>
>> _______________________________________________
>> nginx-devel mailing list
>> nginx-devel at nginx.org
>> http://mailman.nginx.org/mailman/listinfo/nginx-devel
>
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