Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct II
On Thu, Mar 10, 2011 at 08:00:32AM -0800, Andi Kleen wrote: > On Tue, Mar 08, 2011 at 07:31:56PM -0500, Stephen Wilson wrote: > > > > Morally, the question of whether an address lies in a gate vma should be > > asked > > with respect to an mm, not a particular task. > > > > Practically, dropping the dependency on task_struct will help make current > > and > > future operations on mm's more flexible and convenient. In particular, it > > allows some code paths to avoid the need to hold task_lock. > > > > The only architecture this change impacts in any significant way is x86_64. > > The principle change on that architecture is to mirror TIF_IA32 via > > a new flag in mm_context_t. > > The problem is -- you're adding a likely cache miss on mm_struct for > every 32bit compat syscall now, even if they don't need mm_struct > currently (and a lot of them do not) Unless there's a very good > justification to make up for this performance issue elsewhere > (including numbers) this seems like a bad idea. Hmm I see you're only setting it on exec time actually on rereading the patches. I thought you were changing TS_COMPAT which is in the syscall path. Never mind. I have no problems with doing such a change on exec time. -Andi ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct II
On Thu, Mar 10, 2011 at 08:38:09AM -0800, Andi Kleen wrote: > On Thu, Mar 10, 2011 at 08:00:32AM -0800, Andi Kleen wrote: > > On Tue, Mar 08, 2011 at 07:31:56PM -0500, Stephen Wilson wrote: > > > The only architecture this change impacts in any significant way is > > > x86_64. > > > The principle change on that architecture is to mirror TIF_IA32 via > > > a new flag in mm_context_t. > > > > The problem is -- you're adding a likely cache miss on mm_struct for > > every 32bit compat syscall now, even if they don't need mm_struct > > currently (and a lot of them do not) Unless there's a very good > > justification to make up for this performance issue elsewhere > > (including numbers) this seems like a bad idea. > > Hmm I see you're only setting it on exec time actually on rereading > the patches. I thought you were changing TS_COMPAT which is in > the syscall path. > > Never mind. I have no problems with doing such a change on exec > time. OK. Great! Does this mean I have your ACK'ed by or reviewed by? Thanks for taking a look! -- steve ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct II
On Thu, Mar 10, 2011 at 11:54:14AM -0500, Stephen Wilson wrote: > > On Thu, Mar 10, 2011 at 08:38:09AM -0800, Andi Kleen wrote: > > On Thu, Mar 10, 2011 at 08:00:32AM -0800, Andi Kleen wrote: > > > On Tue, Mar 08, 2011 at 07:31:56PM -0500, Stephen Wilson wrote: > > > > The only architecture this change impacts in any significant way is > > > > x86_64. > > > > The principle change on that architecture is to mirror TIF_IA32 via > > > > a new flag in mm_context_t. > > > > > > The problem is -- you're adding a likely cache miss on mm_struct for > > > every 32bit compat syscall now, even if they don't need mm_struct > > > currently (and a lot of them do not) Unless there's a very good > > > justification to make up for this performance issue elsewhere > > > (including numbers) this seems like a bad idea. > > > > Hmm I see you're only setting it on exec time actually on rereading > > the patches. I thought you were changing TS_COMPAT which is in > > the syscall path. > > > > Never mind. I have no problems with doing such a change on exec > > time. > > OK. Great! Does this mean I have your ACK'ed by or reviewed by? I didn't read it all, but the first two patches looked ok. -Andi ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct II
Sorry... I confused them too. It's TS_COMPAT which is problematic. -- Sent from my mobile phone. Please pardon any lack of formatting. Stephen Wilson wrote: On Thu, Mar 10, 2011 at 08:38:09AM -0800, Andi Kleen wrote: > On Thu, Mar 10, 2011 at 08:00:32AM -0800, Andi Kleen wrote: > > On Tue, Mar 08, 2011 at 07:31:56PM -0500, Stephen Wilson wrote: > > > The only architecture this change impacts in any significant way is x86_64. > > > The principle change on that architecture is to mirror TIF_IA32 via > > > a new flag in mm_context_t. > > > > The problem is -- you're adding a likely cache miss on mm_struct for > > every 32bit compat syscall now, even if they don't need mm_struct > > currently (and a lot of them do not) Unless there's a very good > > justification to make up for this performance issue elsewhere > > (including numbers) this seems like a bad idea. > > Hmm I see you're only setting it on exec time actually on rereading > the patches. I thought you were changing TS_COMPAT which is in > the syscall path. > > Never mind. I have no problems with doing such a change on exec > time. OK. Great! Does this mean I have your ACK'e! d by or reviewed by? Thanks for taking a look! -- steve ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
