From: Johannes Weiner <han...@cmpxchg.org> Reads can take a long time, and if anybody needs to take a write lock on the mmap_sem it'll block any subsequent readers to the mmap_sem while the read is outstanding, which could cause long delays. Instead drop the mmap_sem if we do any reads at all.
Signed-off-by: Johannes Weiner <han...@cmpxchg.org> Signed-off-by: Josef Bacik <jo...@toxicpanda.com> --- mm/filemap.c | 119 ++++++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 90 insertions(+), 29 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 52517f28e6f4..1ed35cd99b2c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2366,6 +2366,18 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) EXPORT_SYMBOL(generic_file_read_iter); #ifdef CONFIG_MMU +static struct file *maybe_unlock_mmap_for_io(struct vm_area_struct *vma, int flags) +{ + if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) == FAULT_FLAG_ALLOW_RETRY) { + struct file *file; + + file = get_file(vma->vm_file); + up_read(&vma->vm_mm->mmap_sem); + return file; + } + return NULL; +} + /** * page_cache_read - adds requested page to the page cache if not already there * @file: file to read @@ -2405,23 +2417,28 @@ static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask) * Synchronous readahead happens when we don't even find * a page in the page cache at all. */ -static void do_sync_mmap_readahead(struct vm_area_struct *vma, - struct file_ra_state *ra, - struct file *file, - pgoff_t offset) +static int do_sync_mmap_readahead(struct vm_area_struct *vma, + struct file_ra_state *ra, + struct file *file, + pgoff_t offset, + int flags) { struct address_space *mapping = file->f_mapping; + struct file *fpin; /* If we don't want any read-ahead, don't bother */ if (vma->vm_flags & VM_RAND_READ) - return; + return 0; if (!ra->ra_pages) - return; + return 0; if (vma->vm_flags & VM_SEQ_READ) { + fpin = maybe_unlock_mmap_for_io(vma, flags); page_cache_sync_readahead(mapping, ra, file, offset, ra->ra_pages); - return; + if (fpin) + fput(fpin); + return fpin ? -EAGAIN : 0; } /* Avoid banging the cache line if not needed */ @@ -2433,7 +2450,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, * stop bothering with read-ahead. It will only hurt. */ if (ra->mmap_miss > MMAP_LOTSAMISS) - return; + return 0; + + fpin = maybe_unlock_mmap_for_io(vma, flags); /* * mmap read-around @@ -2442,28 +2461,40 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, ra->size = ra->ra_pages; ra->async_size = ra->ra_pages / 4; ra_submit(ra, mapping, file); + + if (fpin) + fput(fpin); + + return fpin ? -EAGAIN : 0; } /* * Asynchronous readahead happens when we find the page and PG_readahead, * so we want to possibly extend the readahead further.. */ -static void do_async_mmap_readahead(struct vm_area_struct *vma, - struct file_ra_state *ra, - struct file *file, - struct page *page, - pgoff_t offset) +static int do_async_mmap_readahead(struct vm_area_struct *vma, + struct file_ra_state *ra, + struct file *file, + struct page *page, + pgoff_t offset, + int flags) { struct address_space *mapping = file->f_mapping; + struct file *fpin; /* If we don't want any read-ahead, don't bother */ if (vma->vm_flags & VM_RAND_READ) - return; + return 0; if (ra->mmap_miss > 0) ra->mmap_miss--; - if (PageReadahead(page)) - page_cache_async_readahead(mapping, ra, file, - page, offset, ra->ra_pages); + if (!PageReadahead(page)) + return 0; + fpin = maybe_unlock_mmap_for_io(vma, flags); + page_cache_async_readahead(mapping, ra, file, + page, offset, ra->ra_pages); + if (fpin) + fput(fpin); + return fpin ? -EAGAIN : 0; } /** @@ -2479,10 +2510,8 @@ static void do_async_mmap_readahead(struct vm_area_struct *vma, * * vma->vm_mm->mmap_sem must be held on entry. * - * If our return value has VM_FAULT_RETRY set, it's because - * lock_page_or_retry() returned 0. - * The mmap_sem has usually been released in this case. - * See __lock_page_or_retry() for the exception. + * If our return value has VM_FAULT_RETRY set, the mmap_sem has + * usually been released. * * If our return value does not have VM_FAULT_RETRY set, the mmap_sem * has not been released. @@ -2492,11 +2521,13 @@ static void do_async_mmap_readahead(struct vm_area_struct *vma, vm_fault_t filemap_fault(struct vm_fault *vmf) { int error; + struct mm_struct *mm = vmf->vma->vm_mm; struct file *file = vmf->vma->vm_file; struct address_space *mapping = file->f_mapping; struct file_ra_state *ra = &file->f_ra; struct inode *inode = mapping->host; pgoff_t offset = vmf->pgoff; + int flags = vmf->flags; pgoff_t max_off; struct page *page; vm_fault_t ret = 0; @@ -2509,27 +2540,44 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) * Do we have something in the page cache already? */ page = find_get_page(mapping, offset); - if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) { + if (likely(page) && !(flags & FAULT_FLAG_TRIED)) { /* * We found the page, so try async readahead before * waiting for the lock. */ - do_async_mmap_readahead(vmf->vma, ra, file, page, offset); + error = do_async_mmap_readahead(vmf->vma, ra, file, page, offset, vmf->flags); + if (error == -EAGAIN) + goto out_retry_wait; } else if (!page) { /* No page in the page cache at all */ - do_sync_mmap_readahead(vmf->vma, ra, file, offset); - count_vm_event(PGMAJFAULT); - count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); ret = VM_FAULT_MAJOR; + count_vm_event(PGMAJFAULT); + count_memcg_event_mm(mm, PGMAJFAULT); + error = do_sync_mmap_readahead(vmf->vma, ra, file, offset, vmf->flags); + if (error == -EAGAIN) + goto out_retry_wait; retry_find: page = find_get_page(mapping, offset); if (!page) goto no_cached_page; } - if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) { - put_page(page); - return ret | VM_FAULT_RETRY; + if (!trylock_page(page)) { + if (flags & FAULT_FLAG_ALLOW_RETRY) { + if (flags & FAULT_FLAG_RETRY_NOWAIT) + goto out_retry; + up_read(&mm->mmap_sem); + goto out_retry_wait; + } + if (flags & FAULT_FLAG_KILLABLE) { + int ret = __lock_page_killable(page); + + if (ret) { + up_read(&mm->mmap_sem); + goto out_retry; + } + } else + __lock_page(page); } /* Did it get truncated? */ @@ -2607,6 +2655,19 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) /* Things didn't work out. Return zero to tell the mm layer so. */ shrink_readahead_size_eio(file, ra); return VM_FAULT_SIGBUS; + +out_retry_wait: + if (page) { + if (flags & FAULT_FLAG_KILLABLE) + wait_on_page_locked_killable(page); + else + wait_on_page_locked(page); + } + +out_retry: + if (page) + put_page(page); + return ret | VM_FAULT_RETRY; } EXPORT_SYMBOL(filemap_fault); -- 2.14.3