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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
