Hi Kirill, > On Jun 21, 2019, at 5:58 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > On Fri, Jun 14, 2019 at 11:22:04AM -0700, Song Liu wrote: >> This patch is (hopefully) the first step to enable THP for non-shmem >> filesystems. >> >> This patch enables an application to put part of its text sections to THP >> via madvise, for example: >> >> madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE); >> >> We tried to reuse the logic for THP on tmpfs. The following functions are >> renamed to reflect the new functionality: >> >> collapse_shmem() => collapse_file() >> khugepaged_scan_shmem() => khugepaged_scan_file() >> >> Currently, write is not supported for non-shmem THP. This is enforced by >> taking negative i_writecount. Therefore, if file has THP pages in the >> page cache, open() to write will fail. To update/modify the file, the >> user need to remove it first. >> >> An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this >> feature. > > Please document explicitly that the feature opens local DoS attack: any > user with read access to file can block write to the file by using > MADV_HUGEPAGE for a range of the file. > > As is it only has to be used with trusted userspace. > > We also might want to have mount option in addition to Kconfig option to > enable the feature on per-mount basis. This behavior has been removed from v3 to v5. Thanks, Song
