From patchwork Mon Aug 15 20:25:35 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Barry X-Patchwork-Id: 110090 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id C0DD9B6F72 for ; Tue, 16 Aug 2011 06:26:39 +1000 (EST) Received: from localhost ([::1]:44876 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qt3k4-00028z-7x for incoming@patchwork.ozlabs.org; Mon, 15 Aug 2011 16:26:36 -0400 Received: from eggs.gnu.org ([140.186.70.92]:35742) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qt3jw-00028n-UU for qemu-devel@nongnu.org; Mon, 15 Aug 2011 16:26:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Qt3jv-0001L9-74 for qemu-devel@nongnu.org; Mon, 15 Aug 2011 16:26:28 -0400 Received: from exprod6og103.obsmtp.com ([64.18.1.185]:32777) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qt3ju-0001KU-PH for qemu-devel@nongnu.org; Mon, 15 Aug 2011 16:26:27 -0400 Received: from cfexcas02.americas.cray.com ([136.162.34.11]) (using TLSv1) by exprod6ob103.postini.com ([64.18.5.12]) with SMTP ID DSNKTkmAwDoO59AuTyS9npCVGGZ7FnhckHZc@postini.com; Mon, 15 Aug 2011 13:26:26 PDT Received: from lnx-abarry.us.cray.com (172.31.17.80) by cfexcas02.americas.cray.com (172.30.74.226) with Microsoft SMTP Server (TLS) id 8.3.192.1; Mon, 15 Aug 2011 15:25:35 -0500 Message-ID: <4E4980BF.7090801@cray.com> Date: Mon, 15 Aug 2011 15:25:35 -0500 From: Andrew Barry User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100317 SUSE/3.0.4-2.3 Lightning/1.0b1 Thunderbird/3.0.4 MIME-Version: 1.0 To: Hugh Dickins References: <20110811064059.GU6342@yookeroo.fritz.box> <20110813010839.GC30552@yookeroo.fritz.box> In-Reply-To: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6, seldom 2.4 (older, 4) X-Received-From: 64.18.1.185 Cc: "agraf@suse.de" , kvm , "linux-kernel@vger.kernel.org" , Marcelo Tosatti , "qemu-devel@nongnu.org" , David Gibson , Adam Litke , Minchan Kim , Jan Kiszka , Avi Kivity , KOSAKI Motohiro , Andrew Hastings , Paul Mackerras , Andrew Morton , Linus Torvalds , Mel Gorman , KAMEZAWA Hiroyuki , David Gibson Subject: Re: [Qemu-devel] Fix refcounting in hugetlbfs quota handling X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org I've been doing something similar to this last proposal. I put a hugetlbfs_sb_info pointer into page_private, and dropped a reference counter and an active/inactive bit into the hugetlbfs_sb_info struct. At Umount time, the sbinfo is freed, only if the reference count is zero. Otherwise, the last put_quota frees the sbinfo structure. This fixed the race we were seeing between umount and a put_quota from an rdma transaction. I just gave it a cursory test on a 3.0 kernel; it has seen quite a lot more testing on a 2.6.32-derived kernel, with no more hits of the umount race. Does this address the problems you were thinking about? -Andrew Barry @@ -2086,7 +2086,7 @@ static void hugetlb_vm_op_close(struct v if (reserve) { hugetlb_acct_memory(h, -reserve); - hugetlb_put_quota(vma->vm_file->f_mapping, reserve); + hugetlb_put_quota(HUGETLBFS_SB(vma->vm_file->f_mapping->host->i_sb), reserve); } } } @@ -2884,7 +2884,7 @@ int hugetlb_reserve_pages(struct inode * return chg; /* There must be enough filesystem quota for the mapping */ - if (hugetlb_get_quota(inode->i_mapping, chg)) + if (hugetlb_get_quota(HUGETLBFS_SB(inode->i_mapping->host->i_sb), chg)) return -ENOSPC; /* @@ -2893,7 +2893,7 @@ int hugetlb_reserve_pages(struct inode * */ ret = hugetlb_acct_memory(h, chg); if (ret < 0) { - hugetlb_put_quota(inode->i_mapping, chg); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_mapping->host->i_sb), chg); return ret; } @@ -2922,7 +2922,7 @@ void hugetlb_unreserve_pages(struct inod inode->i_blocks -= (blocks_per_huge_page(h) * freed); spin_unlock(&inode->i_lock); - hugetlb_put_quota(inode->i_mapping, (chg - freed)); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_mapping->host->i_sb), (chg - freed)); hugetlb_acct_memory(h, -(chg - freed)); } On 08/15/2011 01:00 PM, Hugh Dickins wrote: > On Sat, 13 Aug 2011, David Gibson wrote: >> On Fri, Aug 12, 2011 at 12:15:21PM -0700, Hugh Dickins wrote: >>> >>> Setting that aside, I think this thing of grabbing a reference to inode >>> for each page just does not work as you wish: when we unlink an inode, >>> all its pages should be freed; but because they are themselves holding >>> references to the inode, it and its pages stick around forever. >> >> Ugh, yes. You're absolutely right. That circular reference will mess >> everything up. Thinking it through and testing fail. >> >>> A quick experiment with your patch versus without confirmed that: >>> meminfo HugePages_Free stayed down with your patch, but went back to >>> HugePages_Total without it. Please check, perhaps I'm just mistaken. >>> >>> Sorry, I've not looked into what a constructive alternative might be; >>> and it's not the first time we've had this difficulty - it came up last >>> year when the ->freepage function was added, that the inode may be gone >>> by the time ->freepage(page) is called. >> >> Ok, so. In fact the quota functions we call at free time only need >> the super block, not the inode per se. If we put a superblock pointer >> instead of an inode pointer in page private, and refcounted that, I >> think that should remove the circular ref. The only reason I didn't >> do it before is that the superblock refcounting functions didn't seem >> to be globally visible in an obvious way. >> >> Does that sound like a reasonable approach? > > That does sound closer to a reaonable approach, but my guess is that it > will suck you into a world of superblock mutexes and semaphores, which > you cannot take at free_huge_page() time. > > It might be necessary to hang your own tiny structure off the superblock, > with one refcount for the superblock, and one for each hugepage attached, > you freeing that structure when the count goes down to zero from either > direction. > > Whatever you do needs testing with lockdep and atomic sleep checks. > > I do dislike tying these separate levels together in such an unusual way, > but it is a difficult problem and I don't know of an easy answer. Maybe > we'll need to find a better answer for other reasons, it does come up > from time to time e.g. recent race between evicting inode and nrpages > going down to 0. > > You might care to take a look at how tmpfs (mm/shmem.c) deals with > the equivalent issue there (sbinfo->used_blocks). But I expect you to > conclude that hugetlbfs cannot afford the kind of approximations that > tmpfs can afford. > > Although I think tmpfs is more correct, to be associating the count > with pagecache (so the count goes down as soon as a page is truncated > or evicted from pagecache), your fewer and huger pages, and reservation > conventions, may well demand that the count stays up until the page is > actually freed back to hugepool. And let's not pretend that what tmpfs > does is wonderful: the strange shmem_recalc_inode() tries its best to > notice when memory pressure has freed clean pages, but it never looks > beyond the inode being accessed at the times it's called. Not at all > satisfactory, but not actually an issue in practice, since we stopped > allocating pages for simple reads from sparse file. I did want to > convert tmpfs to use ->freepage(), but couldn't manage it without > stable mapping - same problem as you have. > > Hugh > -- > 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/ diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 87b6e04..2ed1cca 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -615,8 +615,12 @@ static void hugetlbfs_put_super(struct s struct hugetlbfs_sb_info *sbi = HUGETLBFS_SB(sb); if (sbi) { + sbi->active = HPAGE_INACTIVE; sb->s_fs_info = NULL; - kfree(sbi); + + /*Free only if used quota is zero. */ + if (sbi->used_blocks == 0) + kfree(sbi); } } @@ -851,6 +855,8 @@ hugetlbfs_fill_super(struct super_block sbinfo->free_blocks = config.nr_blocks; sbinfo->max_inodes = config.nr_inodes; sbinfo->free_inodes = config.nr_inodes; + sbinfo->used_blocks = 0; + sbinfo->active = HPAGE_ACTIVE; sb->s_maxbytes = MAX_LFS_FILESIZE; sb->s_blocksize = huge_page_size(config.hstate); sb->s_blocksize_bits = huge_page_shift(config.hstate); @@ -874,30 +880,36 @@ out_free: return -ENOMEM; } -int hugetlb_get_quota(struct address_space *mapping, long delta) +int hugetlb_get_quota(struct hugetlbfs_sb_info *sbinfo, long delta) { int ret = 0; - struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb); - if (sbinfo->free_blocks > -1) { - spin_lock(&sbinfo->stat_lock); - if (sbinfo->free_blocks - delta >= 0) + spin_lock(&sbinfo->stat_lock); + if ((sbinfo->free_blocks == -1) || (sbinfo->free_blocks - delta >= 0)) { + if (sbinfo->free_blocks != -1) sbinfo->free_blocks -= delta; - else - ret = -ENOMEM; - spin_unlock(&sbinfo->stat_lock); + sbinfo->used_blocks += delta; + sbinfo->active = HPAGE_ACTIVE; + } else { + ret = -ENOMEM; } + spin_unlock(&sbinfo->stat_lock); return ret; } -void hugetlb_put_quota(struct address_space *mapping, long delta) +void hugetlb_put_quota(struct hugetlbfs_sb_info *sbinfo, long delta) { - struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb); - - if (sbinfo->free_blocks > -1) { - spin_lock(&sbinfo->stat_lock); + spin_lock(&sbinfo->stat_lock); + if (sbinfo->free_blocks > -1) sbinfo->free_blocks += delta; + sbinfo->used_blocks -= delta; + /* If hugetlbfs_put_super couldn't free sbinfo due to + * an outstanding quota reference, free it now. */ + if ((sbinfo->used_blocks == 0) && (sbinfo->active == HPAGE_INACTIVE)) { + spin_unlock(&sbinfo->stat_lock); + kfree(sbinfo); + } else { spin_unlock(&sbinfo->stat_lock); } } diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 19644e0..8780a91 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -142,11 +142,16 @@ struct hugetlbfs_config { struct hstate *hstate; }; +#define HPAGE_INACTIVE 0 +#define HPAGE_ACTIVE 1 + struct hugetlbfs_sb_info { long max_blocks; /* blocks allowed */ long free_blocks; /* blocks free */ long max_inodes; /* inodes allowed */ long free_inodes; /* inodes free */ + long used_blocks; /* blocks used */ + long active; /* active bit */ spinlock_t stat_lock; struct hstate *hstate; }; @@ -171,8 +176,8 @@ extern const struct file_operations huge extern const struct vm_operations_struct hugetlb_vm_ops; struct file *hugetlb_file_setup(const char *name, size_t size, vm_flags_t acct, struct user_struct **user, int creat_flags); -int hugetlb_get_quota(struct address_space *mapping, long delta); -void hugetlb_put_quota(struct address_space *mapping, long delta); +int hugetlb_get_quota(struct hugetlbfs_sb_info *sbinfo, long delta); +void hugetlb_put_quota(struct hugetlbfs_sb_info *sbinfo, long delta); static inline int is_file_hugepages(struct file *file) { diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dae27ba..cf26ae9 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -533,9 +533,9 @@ static void free_huge_page(struct page * */ struct hstate *h = page_hstate(page); int nid = page_to_nid(page); - struct address_space *mapping; + struct hugetlbfs_sb_info *sbinfo; - mapping = (struct address_space *) page_private(page); + sbinfo = ( struct hugetlbfs_sb_info *) page_private(page); set_page_private(page, 0); page->mapping = NULL; BUG_ON(page_count(page)); @@ -551,8 +551,8 @@ static void free_huge_page(struct page * enqueue_huge_page(h, page); } spin_unlock(&hugetlb_lock); - if (mapping) - hugetlb_put_quota(mapping, 1); + if (sbinfo) + hugetlb_put_quota(sbinfo, 1); } static void prep_new_huge_page(struct hstate *h, struct page *page, int nid) @@ -1035,7 +1035,7 @@ static struct page *alloc_huge_page(stru if (chg < 0) return ERR_PTR(-VM_FAULT_OOM); if (chg) - if (hugetlb_get_quota(inode->i_mapping, chg)) + if (hugetlb_get_quota(HUGETLBFS_SB(inode->i_mapping->host->i_sb), chg)) return ERR_PTR(-VM_FAULT_SIGBUS); spin_lock(&hugetlb_lock); @@ -1045,12 +1045,12 @@ static struct page *alloc_huge_page(stru if (!page) { page = alloc_buddy_huge_page(h, NUMA_NO_NODE); if (!page) { - hugetlb_put_quota(inode->i_mapping, chg); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_mapping->host->i_sb), chg); return ERR_PTR(-VM_FAULT_SIGBUS); } } - set_page_private(page, (unsigned long) mapping); + set_page_private(page, (unsigned long) HUGETLBFS_SB(inode->i_mapping->host->i_sb)); vma_commit_reservation(h, vma, addr);