Messages in this thread | | | Date | Thu, 23 Feb 2023 01:31:54 +0000 | Subject | Re: [RFC PATCH 0/2] Add flag as THP allocation hint for memfd_restricted() syscall | From | Ackerley Tng <> |
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Yuan Yao <yuan.yao@linux.intel.com> writes:
> On Sat, Feb 18, 2023 at 12:43:00AM +0000, Ackerley Tng wrote: >> Hello,
>> This patchset builds upon the memfd_restricted() system call that has >> been discussed in the ‘KVM: mm: fd-based approach for supporting KVM’ >> patch series, at >> https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/#m7e944d7892afdd1d62a03a287bd488c56e377b0c
>> The tree can be found at: >> https://github.com/googleprodkernel/linux-cc/tree/restrictedmem-rmfd-hugepage
>> Following the RFC to provide mount for memfd_restricted() syscall at >> https://lore.kernel.org/lkml/cover.1676507663.git.ackerleytng@google.com/T/#u, >> this patchset adds the RMFD_HUGEPAGE flag to the memfd_restricted() >> syscall, which will hint the kernel to use Transparent HugePages to >> back restrictedmem pages.
>> This supplements the interface proposed earlier, which requires the >> creation of a tmpfs mount to be passed to memfd_restricted(), with a >> more direct per-file hint.
>> Dependencies:
>> + Sean’s iteration of the ‘KVM: mm: fd-based approach for supporting >> KVM’ patch series at >> https://github.com/sean-jc/linux/tree/x86/upm_base_support >> + Proposed fix for restrictedmem_getattr() as mentioned on the mailing >> list at >> >> https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com/ >> + Hugh’s patch: >> >> https://lore.kernel.org/lkml/c140f56a-1aa3-f7ae-b7d1-93da7d5a3572@google.com/, >> which provides functionality in shmem that reads the VM_HUGEPAGE >> flag in key functions shmem_is_huge() and shmem_get_inode()
> Will Hugh's patch be merged into 6.3 ? I didn't find it in 6.2-rc8. > IMHO this patch won't work without Hugh's patch, or at least need > another way, e.g. HMEM_SB(inode->i_sb)->huge.
Hugh's patch is still pending discussion and may not be merged so soon. These patches will not work without Hugh's patch.
I would like to understand what the community thinks of the proposed interface (RMFD_HUGEPAGE flag, passed to the memfd_restricted() syscall). If this interface is favorably received, we can definitely find another way for shmem to support this interface.
If I understand correctly, SHMEM_SB(inode->i_sb)->huge checks the state of hugepage-ness for the superblock. Since the proposed interface will only affect a single file, we will need something closer to
bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode, pgoff_t index, bool shmem_huge_force) { ...
if (SHMEM_I(inode)->flags & VM_HUGEPAGE) return true;
... }
from Hugh's patch.
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