Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754673Ab1BALV6 (ORCPT ); Tue, 1 Feb 2011 06:21:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39224 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754631Ab1BALVy (ORCPT ); Tue, 1 Feb 2011 06:21:54 -0500 From: Gleb Natapov To: avi@redhat.com, mtosatti@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds , Rik van Riel , Hugh Dickins , Andrew Morton Subject: [PATCH 1/2] Allow GUP to fail instead of waiting on a page. Date: Tue, 1 Feb 2011 13:21:46 +0200 Message-Id: <1296559307-14637-2-git-send-email-gleb@redhat.com> In-Reply-To: <1296559307-14637-1-git-send-email-gleb@redhat.com> References: <1296559307-14637-1-git-send-email-gleb@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3525 Lines: 91 GUP user may want to try to acquire a reference to a page if it is already in memory, but not if IO, to bring it in, is needed. For example KVM may tell vcpu to schedule another guest process if current one is trying to access swapped out page. Meanwhile, the page will be swapped in and the guest process, that depends on it, will be able to run again. This patch adds FAULT_FLAG_RETRY_NOWAIT (suggested by Linus) and FOLL_NOWAIT follow_page flags. FAULT_FLAG_RETRY_NOWAIT, when used in conjunction with VM_FAULT_ALLOW_RETRY, indicates to handle_mm_fault that it shouldn't drop mmap_sem and wait on a page, but return VM_FAULT_RETRY instead. Signed-off-by: Gleb Natapov CC: Linus Torvalds CC: Rik van Riel CC: Hugh Dickins CC: Andrew Morton --- include/linux/mm.h | 2 ++ mm/filemap.c | 6 ++++-- mm/memory.c | 5 ++++- 3 files changed, 10 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 9c3a7c8..fa5e562 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -151,6 +151,7 @@ extern pgprot_t protection_map[16]; #define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */ #define FAULT_FLAG_MKWRITE 0x04 /* Fault was mkwrite of existing pte */ #define FAULT_FLAG_ALLOW_RETRY 0x08 /* Retry fault if blocking */ +#define FAULT_FLAG_RETRY_NOWAIT 0x10 /* Don't drop mmap_sem and wait when retrying */ /* * This interface is used by x86 PAT code to identify a pfn mapping that is @@ -1532,6 +1533,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address, #define FOLL_GET 0x04 /* do get_page on page */ #define FOLL_DUMP 0x08 /* give error on hole if it would be zero */ #define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */ +#define FOLL_NOWAIT 0x20 /* return if disk transfer is needed */ #define FOLL_MLOCK 0x40 /* mark page as mlocked */ #define FOLL_SPLIT 0x80 /* don't return transhuge pages, split them */ #define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */ diff --git a/mm/filemap.c b/mm/filemap.c index 83a45d3..312b6eb 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -621,8 +621,10 @@ int __lock_page_or_retry(struct page *page, struct mm_struct *mm, __lock_page(page); return 1; } else { - up_read(&mm->mmap_sem); - wait_on_page_locked(page); + if (!(flags & FAULT_FLAG_RETRY_NOWAIT)) { + up_read(&mm->mmap_sem); + wait_on_page_locked(page); + } return 0; } } diff --git a/mm/memory.c b/mm/memory.c index e7c9a99..a52a3e6 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1569,6 +1569,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, fault_flags |= FAULT_FLAG_WRITE; if (nonblocking) fault_flags |= FAULT_FLAG_ALLOW_RETRY; + if (foll_flags & FOLL_NOWAIT) + fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT); ret = handle_mm_fault(mm, vma, start, fault_flags); @@ -1595,7 +1597,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, tsk->min_flt++; if (ret & VM_FAULT_RETRY) { - *nonblocking = 0; + if (nonblocking) + *nonblocking = 0; return i; } -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/