v2 has been uploaded with performance testing results: https://lore.kernel.org/patchwork/patch/1408266/ On Mon, Mar 22, 2021 at 2:59 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. > > Restricting the use of THPs to executable mappings eliminates the risk that > a read-only file later opened for write would encounter significant > latencies due to page cache truncation. > > The ld linker flag '-z max-page-size=(hugepage size)' can be used to > produce executables with the necessary layout. The dynamic linker must > map these file's segments at a hugepage size aligned vma for the mapping to > be backed with THPs. > > Signed-off-by: Collin Fijalkovich <cfijalkovich@xxxxxxxxxx> > --- > fs/open.c | 13 +++++++++++-- > mm/khugepaged.c | 16 +++++++++++++++- > 2 files changed, 26 insertions(+), 3 deletions(-) > > diff --git a/fs/open.c b/fs/open.c > index e53af13b5835..f76e960d10ea 100644 > --- a/fs/open.c > +++ b/fs/open.c > @@ -852,8 +852,17 @@ static int do_dentry_open(struct file *f, > * XXX: Huge page cache doesn't support writing yet. Drop all page > * cache for this file before processing writes. > */ > - if ((f->f_mode & FMODE_WRITE) && filemap_nr_thps(inode->i_mapping)) > - truncate_pagecache(inode, 0); > + if (f->f_mode & FMODE_WRITE) { > + /* > + * Paired with smp_mb() in collapse_file() to ensure nr_thps > + * is up to date and the update to i_writecount by > + * get_write_access() is visible. Ensures subsequent insertion > + * of THPs into the page cache will fail. > + */ > + smp_mb(); > + if (filemap_nr_thps(inode->i_mapping)) > + truncate_pagecache(inode, 0); > + } > > return 0; > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index a7d6cb912b05..4c7cc877d5e3 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -459,7 +459,8 @@ static bool hugepage_vma_check(struct vm_area_struct *vma, > > /* Read-only file mappings need to be aligned for THP to work. */ > if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file && > - (vm_flags & VM_DENYWRITE)) { > + !inode_is_open_for_write(vma->vm_file->f_inode) && > + (vm_flags & VM_EXEC)) { > return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, > HPAGE_PMD_NR); > } > @@ -1872,6 +1873,19 @@ static void collapse_file(struct mm_struct *mm, > else { > __mod_lruvec_page_state(new_page, NR_FILE_THPS, nr); > filemap_nr_thps_inc(mapping); > + /* > + * Paired with smp_mb() in do_dentry_open() to ensure > + * i_writecount is up to date and the update to nr_thps is > + * visible. Ensures the page cache will be truncated if the > + * file is opened writable. > + */ > + smp_mb(); > + if (inode_is_open_for_write(mapping->host)) { > + result = SCAN_FAIL; > + __mod_lruvec_page_state(new_page, NR_FILE_THPS, -nr); > + filemap_nr_thps_dec(mapping); > + goto xa_locked; > + } > } > > if (nr_none) { > -- > 2.31.0.rc2.261.g7f71774620-goog >
