netdev - Re: [PATCH] tcp: restore correct limit

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Date:	Tue, 10 Apr 2012 12:40:36 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	monstr@...str.eu, netdev@...r.kernel.org,
	John Williams <john.williams@...alogix.com>,
	David Miller <davem@...emloft.net>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [PATCH] tcp: restore correct limit

On Tue, 2012-04-10 at 18:29 +0800, Jason Wang wrote:
> On 04/10/2012 06:14 PM, Michal Simek wrote:
> > On 04/10/2012 12:03 PM, Eric Dumazet wrote:
> >> Commit c43b874d5d714f (tcp: properly initialize tcp memory limits)
> >> added a regression on machines with low amount of memory, since sockets
> >> cant use 1/128 of memory but 1/1024
> >>
> >> Fix this to match comment and previous behavior.
> >>
> >> Signed-off-by: Eric Dumazet<eric.dumazet@...il.com>
> >> Cc: Jason Wang<jasowang@...hat.com>
> >> Cc: Glauber Costa<glommer@...allels.com>
> >> ---
> >>   net/ipv4/tcp.c |    2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> >> index 5d54ed3..67d726e 100644
> >> --- a/net/ipv4/tcp.c
> >> +++ b/net/ipv4/tcp.c
> >> @@ -3302,7 +3302,7 @@ void __init tcp_init(void)
> >>
> >>       tcp_init_mem(&init_net);
> >>       /* Set per-socket limits to no more than 1/128 the pressure 
> >> threshold */
> >> -    limit = nr_free_buffer_pages()<<  (PAGE_SHIFT - 10);
> >> +    limit = nr_free_buffer_pages()<<  (PAGE_SHIFT - 7);
> >>       limit = max(limit, 128UL);
> >>       max_share = min(4UL*1024*1024, limit);
> >>
> >
> > hw design with csum is also much better.
> > Tested-by: Michal Simek <monstr@...str.eu>
> >
> > Thanks for help,
> > Michal
> >
> >
> >
> >
> >
> Hi Michal and Eric:
> 
> Which version of kernel did you test, did you try the newest kernel? The 
> reason I use (PAGE_SHIFT - 10) is in the commit before 3dc43e3, the 
> limit were calculated with:
> 
>      limit = nr_free_buffer_pages() / 8;
>      limit = max(limit, 128UL);
> ...
>      limit = ((unsigned long)sysctl_tcp_mem[1]) << (PAGE_SHIFT - 7);
> 
> So the rmem should be ok. But there's a defect (which I think does 
> affect the regression) of my patch would could cause limit that we 
> should shift after comparing with 128UL like:
> 
>      limit = nr_free_buffer_pages() / 8;
>      limit = max(limit, 128UL) << (PAGE_SHIFT - 7);
> 
> Is anything I miss?
> 

Yes, probably.

Maybe you should check what was the situation on 2.6 kernels.

Your commit did not completely fix the 4acb41903b2 one

I dont feel its necessary to put in the changelog the complete bug
history, since your commit does the needed tracking.



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