> On Mar 23, 2021, at 10:13 AM, Collin Fijalkovich <cfijalkovich@xxxxxxxxxx> wrote: > > Question: when we use this on shared library, the library is still > writable. When the > shared library is opened for write, these pages will refault in as 4kB > pages, right? > > That's correct, while a file is opened for write it will refault into 4kB pages and block use of THPs. Once all writers complete (i_writecount <=0), the file can fault into THPs again and khugepaged can collapse existing page ranges provided that it can successfully allocate new huge pages. Will it be a problem if a slow writer (say a slow scp) writes to the shared library while the shared library is in use? Thanks, Song > > From, > Collin > > On Mon, Mar 22, 2021 at 4:55 PM Song Liu <song@xxxxxxxxxx> wrote: > On Mon, Mar 22, 2021 at 3:00 PM Collin Fijalkovich > <cfijalkovich@xxxxxxxxxx> wrote: > > > > Transparent huge pages are supported for read-only non-shmem filesystems, > > but are only used for vmas with VM_DENYWRITE. This condition ensures that > > file THPs are protected from writes while an application is running > > (ETXTBSY). Any existing file THPs are then dropped from the page cache > > when a file is opened for write in do_dentry_open(). Since sys_mmap > > ignores MAP_DENYWRITE, this constrains the use of file THPs to vmas > > produced by execve(). > > > > Systems that make heavy use of shared libraries (e.g. Android) are unable > > to apply VM_DENYWRITE through the dynamic linker, preventing them from > > benefiting from the resultant reduced contention on the TLB. > > > > This patch reduces the constraint on file THPs allowing use with any > > executable mapping from a file not opened for write (see > > inode_is_open_for_write()). It also introduces additional conditions to > > ensure that files opened for write will never be backed by file THPs. > > Thanks for working on this. We could also use this in many data center > workloads. > > Question: when we use this on shared library, the library is still > writable. When the > shared library is opened for write, these pages will refault in as 4kB > pages, right? > > Thanks, > Song
