Messages in this thread | | | Date | Thu, 15 Nov 2012 11:56:05 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON |
| |
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?
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.
Hugh
| |