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 wils...@start.ca 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 viaa 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
