Messages in this thread | | | Date | Mon, 28 Sep 2009 12:45:35 +1000 | From | Nigel Cunningham <> | Subject | Re: No more bits in vm_area_struct's vm_flags. |
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Hi.
KAMEZAWA Hiroyuki wrote: > On Fri, 25 Sep 2009 18:34:56 +1000 > Nigel Cunningham <ncunningham@crca.org.au> wrote: >> Hi. >> >> KAMEZAWA Hiroyuki wrote: >>>> I have some code in TuxOnIce that needs a bit too (explicitly mark the >>>> VMA as needing to be atomically copied, for GEM objects), and am not >>>> sure what the canonical way to proceed is. Should a new unsigned long be >>>> added? The difficulty I see with that is that my flag was used in >>>> shmem_file_setup's flags parameter (drm_gem_object_alloc), so that >>>> function would need an extra parameter too.. >>> Hmm, how about adding vma->vm_flags2 ? >> The difficulty there is that some functions pass these flags as arguments. >> > Ah yes. But I wonder some special flags, which is rarey used, can be moved > to vm_flags2... > > For example, > > #define VM_SEQ_READ 0x00008000 /* App will access data sequentially */ > #define VM_RAND_READ 0x00010000 /* App will not benefit from clustered reads */ > are all capsuled under > mm.h > 117 #define VM_READHINTMASK (VM_SEQ_READ | VM_RAND_READ) > 118 #define VM_ClearReadHint(v) (v)->vm_flags &= ~VM_READHINTMASK > 119 #define VM_NormalReadHint(v) (!((v)->vm_flags & VM_READHINTMASK)) > 120 #define VM_SequentialReadHint(v) ((v)->vm_flags & VM_SEQ_READ) > 121 #define VM_RandomReadHint(v) ((v)->vm_flags & VM_RAND_READ) > > Or > > 105 #define VM_PFN_AT_MMAP 0x40000000 /* PFNMAP vma that is fully mapped at mmap time */ > is only used under special situation. > > etc.. > > They'll be able to be moved to other(new) flag field, IIUC.
I'm working on a patch to do this, and am looking at is_mergeable_vma, which is invoked via can_vma_merge_after from vma_merge from madvise_behaviour (which potentially modifies these hint flags). Should those hints be considered in that function? (Do I need to pass the hints in as well and check they're equal?)
By the way, VM_ClearReadHint and VM_NormalReadHint are currently unused. madvise_behaviour manipulates the flags directly (in preparing potential replacement values). Not sure if something should be done about that.
By the way #2, in response to the later message in this thread, I'm calling the new var vma->vm_hints, and have put it at the end of the struct at the moment. Is that a good place?
Regards,
Nigel
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