Messages in this thread | | | Date | Fri, 16 Nov 2012 08:40:14 +0800 | From | Jaegeuk Hanse <> | Subject | Re: [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON |
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On 11/16/2012 03:56 AM, Hugh Dickins wrote: > Offtopic... > > On Thu, 15 Nov 2012, Jaegeuk Hanse wrote: >> Another question. Why the function shmem_fallocate which you add to kernel >> need call shmem_getpage? > Because shmem_getpage(_gfp) is where shmem's > page lookup and allocation complexities are handled. > > I assume the question behind your question is: why does shmem actually > allocate pages for its fallocate, instead of just reserving the space?
Yeah, this is what I want to know.
> > I did play with just reserving the space, with more special entries in > the radix_tree to note the reservations made. It should be doable for > the vm_enough_memory and sbinfo->used_blocks reservations. > > What absolutely deterred me from taking that path was the mem_cgroup > case: shmem and swap and memcg are not easy to get working right together, > and nobody would thank me for complicating memcg just for shmem_fallocate. > > By allocating pages, the pre-existing memcg code just works; if we used > reservations instead, we would have to track their memcg charges in some > additional new way. I see no justification for that complication.
Oh, I see, thanks Hugh. :-)
> Hugh
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