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[24.61.119.116]) by smtp.gmail.com with ESMTPSA id u8-20020ac80508000000b0039cc47752casm9565800qtg.77.2022.11.23.04.32.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Nov 2022 04:32:35 -0800 (PST) Date: Wed, 23 Nov 2022 07:32:41 -0500 From: Brian Foster To: Lukas Czerner Cc: "Darrick J. Wong" , Hugh Dickins , Jan Kara , Eric Sandeen , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 1/3] quota: add quota in-memory format support Message-ID: References: <20221121142854.91109-1-lczerner@redhat.com> <20221121142854.91109-2-lczerner@redhat.com> <20221122090448.x2vouglhpnh75exh@fedora> <20221123095227.ilii5htnlh3o6wil@fedora> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221123095227.ilii5htnlh3o6wil@fedora> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Nov 23, 2022 at 10:52:27AM +0100, Lukas Czerner wrote: > On Tue, Nov 22, 2022 at 10:23:57AM -0500, Brian Foster wrote: > > On Tue, Nov 22, 2022 at 10:04:48AM +0100, Lukas Czerner wrote: > > > On Mon, Nov 21, 2022 at 09:48:18AM -0800, Darrick J. Wong wrote: > > > > On Mon, Nov 21, 2022 at 03:28:52PM +0100, Lukas Czerner wrote: > > > > > In memory quota format relies on quota infrastructure to store dquot > > > > > information for us. While conventional quota formats for file systems > > > > > with persistent storage can load quota information into dquot from the > > > > > storage on-demand and hence quota dquot shrinker can free any dquot that > > > > > is not currently being used, it must be avoided here. Otherwise we can > > > > > lose valuable information, user provided limits, because there is no > > > > > persistent storage to load the information from afterwards. > > > > > > > > > > One information that in-memory quota format needs to keep track of is a > > > > > sorted list of ids for each quota type. This is done by utilizing an rb > > > > > tree which root is stored in mem_dqinfo->dqi_priv for each quota type. > > > > > > > > > > This format can be used to support quota on file system without persistent > > > > > storage such as tmpfs. > > > > > > > > > > Signed-off-by: Lukas Czerner > > > > > --- > > > > > fs/quota/Kconfig | 8 ++ > > > > > fs/quota/Makefile | 1 + > > > > > fs/quota/dquot.c | 3 + > > > > > fs/quota/quota_mem.c | 260 +++++++++++++++++++++++++++++++++++++ > > > > > include/linux/quota.h | 7 +- > > > > > include/uapi/linux/quota.h | 1 + > > > > > 6 files changed, 279 insertions(+), 1 deletion(-) > > > > > create mode 100644 fs/quota/quota_mem.c > > > > > > > > > > diff --git a/fs/quota/Kconfig b/fs/quota/Kconfig > > > > > index b59cd172b5f9..8ea9656ca37b 100644 > > > > > --- a/fs/quota/Kconfig > > > > > +++ b/fs/quota/Kconfig > > > > > @@ -67,6 +67,14 @@ config QFMT_V2 > > > > > also supports 64-bit inode and block quota limits. If you need this > > > > > functionality say Y here. > > > > > > > > > > +config QFMT_MEM > > > > > + tristate "Quota in-memory format support " > > > > > + depends on QUOTA > > > > > + help > > > > > + This config option enables kernel support for in-memory quota > > > > > + format support. Useful to support quota on file system without > > > > > + permanent storage. If you need this functionality say Y here. > > > > > + > > > > > config QUOTACTL > > > > > bool > > > > > default n > > > > > diff --git a/fs/quota/Makefile b/fs/quota/Makefile > > > > > index 9160639daffa..935be3f7b731 100644 > > > > > --- a/fs/quota/Makefile > > > > > +++ b/fs/quota/Makefile > > > > > @@ -5,3 +5,4 @@ obj-$(CONFIG_QFMT_V2) += quota_v2.o > > > > > obj-$(CONFIG_QUOTA_TREE) += quota_tree.o > > > > > obj-$(CONFIG_QUOTACTL) += quota.o kqid.o > > > > > obj-$(CONFIG_QUOTA_NETLINK_INTERFACE) += netlink.o > > > > > +obj-$(CONFIG_QFMT_MEM) += quota_mem.o > > > > > diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c > > > > > index 0427b44bfee5..f1a7a03632a2 100644 > > > > > --- a/fs/quota/dquot.c > > > > > +++ b/fs/quota/dquot.c > > > > > @@ -736,6 +736,9 @@ dqcache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > > > > > spin_lock(&dq_list_lock); > > > > > while (!list_empty(&free_dquots) && sc->nr_to_scan) { > > > > > dquot = list_first_entry(&free_dquots, struct dquot, dq_free); > > > > > + if (test_bit(DQ_NO_SHRINK_B, &dquot->dq_flags) && > > > > > + !test_bit(DQ_FAKE_B, &dquot->dq_flags)) > > > > > + continue; > > > > > remove_dquot_hash(dquot); > > > > > remove_free_dquot(dquot); > > > > > remove_inuse(dquot); > > > > > diff --git a/fs/quota/quota_mem.c b/fs/quota/quota_mem.c > > > > > new file mode 100644 > > > > > index 000000000000..7d5e82122143 > > > > > --- /dev/null > > > > > +++ b/fs/quota/quota_mem.c > > > > > @@ -0,0 +1,260 @@ > > > > > +// SPDX-License-Identifier: GPL-2.0-only > > > > > +/* > > > > > + * In memory quota format relies on quota infrastructure to store dquot > > > > > + * information for us. While conventional quota formats for file systems > > > > > + * with persistent storage can load quota information into dquot from the > > > > > + * storage on-demand and hence quota dquot shrinker can free any dquot > > > > > + * that is not currently being used, it must be avoided here. Otherwise we > > > > > + * can lose valuable information, user provided limits, because there is > > > > > + * no persistent storage to load the information from afterwards. > > > > > > > > Hmm. dquots can't /ever/ be reclaimed? struct dquot is ~256 bytes, and > > > > assuming 32-bit uids, the upper bound on dquot usage is 2^(32+8) bytes > > > > == 1TB of memory usage? Once allocated, you'd have to reboot the whole > > > > machine to get that memory back? > > > > > > Hi Darrick, > > > > > > maybe there are some improvements to the documentation to be made. The > > > dquots will be freed on unmount as it would normaly. Also only dquots > > > containing actual user modified limits, so only dquots that are not > > > DQ_FAKE_B are prevented to be reclaimed by a shrinker see the condition in > > > dqcache_shrink_scan(). > > > > > > > > > > > Would it be wise to "persist" dquot contents to a (private) tmpfs file > > > > to facilitate incore dquot reclaim? The tmpfs file data can be paged > > > > out, or even punched if all the dquot records in that page go back to > > > > default settings. > > > > > > The dquot will be flagged as DQ_FAKE_B once the limits are set to 0. But > > > when I think about it this pose a problem with the default quota limits > > > because that would change the limits to the defaults once the dquot is > > > reclaimed and then allocated again. This can be solved by making a > > > custom .set_dqblk(). > > > > > > > Hi Lukas, > > > > I'm a little confused.. does the above mean the dquot limit would have > > to be explicitly set to 0 by the admin in order to be reclaimed, even > > though that limit would be initialized to some non-zero value via the > > mount option? If so, wouldn't we want the ability to reclaim a dquot > > when the usage counts go down to zero (i.e., so the user/group/whatever > > for the dquot no longer has any tmpfs inode/block footprint), assuming > > the limit hasn't also been modified from the initial defaults? > > By creating a custom ->set_dqblk() in shmem we can make sure that the > dquot is non-reclaimable (set DQ_NO_SHRINK_B) *only* if the limits have > been set by the user to anything other than the defaults (defaults being > either 0, or value specified by the mount option). Also > DQ_NO_SHRINK_B can't be set on ->dqblk_read() and the condition in > dqcache_shrink_scan() would only test DQ_NO_SHRINK_B. Does it make more > sense to you? > Ok. Yes, I think I get the general idea. Thanks for the info. Brian > This is something I'd have to do for v3. Sorry for the confusion. > > Thanks! > -Lukas > > > > > Brian > > > > > Other than this problem, does this address your concern about dquot > > > reclaim? > > > > > > Thanks! > > > -Lukas > > > > > > > > > > > --D > > > > > > > > > + * > > > > > + * One information that in-memory quota format needs to keep track of is > > > > > + * a sorted list of ids for each quota type. This is done by utilizing > > > > > + * an rb tree which root is stored in mem_dqinfo->dqi_priv for each quota > > > > > + * type. > > > > > + * > > > > > + * This format can be used to support quota on file system without persistent > > > > > + * storage such as tmpfs. > > > > > + */ > > > > > +#include > > > > > +#include > > > > > +#include > > > > > +#include > > > > > +#include > > > > > +#include > > > > > +#include > > > > > +#include > > > > > + > > > > > +#include > > > > > +#include > > > > > + > > > > > +MODULE_AUTHOR("Lukas Czerner"); > > > > > +MODULE_DESCRIPTION("Quota in-memory format support"); > > > > > +MODULE_LICENSE("GPL"); > > > > > + > > > > > +/* > > > > > + * The following constants define the amount of time given a user > > > > > + * before the soft limits are treated as hard limits (usually resulting > > > > > + * in an allocation failure). The timer is started when the user crosses > > > > > + * their soft limit, it is reset when they go below their soft limit. > > > > > + */ > > > > > +#define MAX_IQ_TIME 604800 /* (7*24*60*60) 1 week */ > > > > > +#define MAX_DQ_TIME 604800 /* (7*24*60*60) 1 week */ > > > > > + > > > > > +struct quota_id { > > > > > + struct rb_node node; > > > > > + qid_t id; > > > > > +}; > > > > > + > > > > > +static int mem_check_quota_file(struct super_block *sb, int type) > > > > > +{ > > > > > + /* There is no real quota file, nothing to do */ > > > > > + return 1; > > > > > +} > > > > > + > > > > > +/* > > > > > + * There is no real quota file. Just allocate rb_root for quota ids and > > > > > + * set limits > > > > > + */ > > > > > +static int mem_read_file_info(struct super_block *sb, int type) > > > > > +{ > > > > > + struct quota_info *dqopt = sb_dqopt(sb); > > > > > + struct mem_dqinfo *info = &dqopt->info[type]; > > > > > + int ret = 0; > > > > > + > > > > > + down_read(&dqopt->dqio_sem); > > > > > + if (info->dqi_fmt_id != QFMT_MEM_ONLY) { > > > > > + ret = -EINVAL; > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > + info->dqi_priv = kzalloc(sizeof(struct rb_root), GFP_NOFS); > > > > > + if (!info->dqi_priv) { > > > > > + ret = -ENOMEM; > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > + /* > > > > > + * Used space is stored as unsigned 64-bit value in bytes but > > > > > + * quota core supports only signed 64-bit values so use that > > > > > + * as a limit > > > > > + */ > > > > > + info->dqi_max_spc_limit = 0x7fffffffffffffffLL; /* 2^63-1 */ > > > > > + info->dqi_max_ino_limit = 0x7fffffffffffffffLL; > > > > > + > > > > > + info->dqi_bgrace = MAX_DQ_TIME; > > > > > + info->dqi_igrace = MAX_IQ_TIME; > > > > > + info->dqi_flags = 0; > > > > > + > > > > > +out_unlock: > > > > > + up_read(&dqopt->dqio_sem); > > > > > + return ret; > > > > > +} > > > > > + > > > > > +static int mem_write_file_info(struct super_block *sb, int type) > > > > > +{ > > > > > + /* There is no real quota file, nothing to do */ > > > > > + return 0; > > > > > +} > > > > > + > > > > > +/* > > > > > + * Free all the quota_id entries in the rb tree and rb_root. > > > > > + */ > > > > > +static int mem_free_file_info(struct super_block *sb, int type) > > > > > +{ > > > > > + struct mem_dqinfo *info = &sb_dqopt(sb)->info[type]; > > > > > + struct rb_root *root = info->dqi_priv; > > > > > + struct quota_id *entry; > > > > > + struct rb_node *node; > > > > > + > > > > > + info->dqi_priv = NULL; > > > > > + node = rb_first(root); > > > > > + while (node) { > > > > > + entry = rb_entry(node, struct quota_id, node); > > > > > + node = rb_next(&entry->node); > > > > > + > > > > > + rb_erase(&entry->node, root); > > > > > + kfree(entry); > > > > > + } > > > > > + > > > > > + kfree(root); > > > > > + return 0; > > > > > +} > > > > > + > > > > > +/* > > > > > + * There is no real quota file, nothing to read. Just insert the id in > > > > > + * the rb tree. > > > > > + */ > > > > > +static int mem_read_dquot(struct dquot *dquot) > > > > > +{ > > > > > + struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type); > > > > > + struct rb_node **n = &((struct rb_root *)info->dqi_priv)->rb_node; > > > > > + struct rb_node *parent = NULL, *new_node = NULL; > > > > > + struct quota_id *new_entry, *entry; > > > > > + qid_t id = from_kqid(&init_user_ns, dquot->dq_id); > > > > > + struct quota_info *dqopt = sb_dqopt(dquot->dq_sb); > > > > > + int ret = 0; > > > > > + > > > > > + down_write(&dqopt->dqio_sem); > > > > > + > > > > > + while (*n) { > > > > > + parent = *n; > > > > > + entry = rb_entry(parent, struct quota_id, node); > > > > > + > > > > > + if (id < entry->id) > > > > > + n = &(*n)->rb_left; > > > > > + else if (id > entry->id) > > > > > + n = &(*n)->rb_right; > > > > > + else > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > + new_entry = kmalloc(sizeof(struct quota_id), GFP_NOFS); > > > > > + if (!new_entry) { > > > > > + ret = -ENOMEM; > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > + new_entry->id = id; > > > > > + new_node = &new_entry->node; > > > > > + rb_link_node(new_node, parent, n); > > > > > + rb_insert_color(new_node, (struct rb_root *)info->dqi_priv); > > > > > + dquot->dq_off = 1; > > > > > + /* > > > > > + * Make sure dquot is never released by a shrinker because we > > > > > + * rely on quota infrastructure to store mem_dqblk in dquot. > > > > > + */ > > > > > + set_bit(DQ_NO_SHRINK_B, &dquot->dq_flags); > > > > > + set_bit(DQ_FAKE_B, &dquot->dq_flags); > > > > > + > > > > > +out_unlock: > > > > > + up_write(&dqopt->dqio_sem); > > > > > + return ret; > > > > > +} > > > > > + > > > > > +static int mem_write_dquot(struct dquot *dquot) > > > > > +{ > > > > > + /* There is no real quota file, nothing to do */ > > > > > + return 0; > > > > > +} > > > > > + > > > > > +static int mem_release_dquot(struct dquot *dquot) > > > > > +{ > > > > > + /* > > > > > + * Everything is in memory only, release once we're done with > > > > > + * quota via mem_free_file_info(). > > > > > + */ > > > > > + return 0; > > > > > +} > > > > > + > > > > > +static int mem_get_next_id(struct super_block *sb, struct kqid *qid) > > > > > +{ > > > > > + struct mem_dqinfo *info = sb_dqinfo(sb, qid->type); > > > > > + struct rb_node *node = ((struct rb_root *)info->dqi_priv)->rb_node; > > > > > + qid_t id = from_kqid(&init_user_ns, *qid); > > > > > + struct quota_info *dqopt = sb_dqopt(sb); > > > > > + struct quota_id *entry = NULL; > > > > > + int ret = 0; > > > > > + > > > > > + down_read(&dqopt->dqio_sem); > > > > > + while (node) { > > > > > + entry = rb_entry(node, struct quota_id, node); > > > > > + > > > > > + if (id < entry->id) > > > > > + node = node->rb_left; > > > > > + else if (id > entry->id) > > > > > + node = node->rb_right; > > > > > + else > > > > > + goto got_next_id; > > > > > + } > > > > > + > > > > > + if (!entry) { > > > > > + ret = -ENOENT; > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > + if (id > entry->id) { > > > > > + node = rb_next(&entry->node); > > > > > + if (!node) { > > > > > + ret = -ENOENT; > > > > > + goto out_unlock; > > > > > + } > > > > > + entry = rb_entry(node, struct quota_id, node); > > > > > + } > > > > > + > > > > > +got_next_id: > > > > > + *qid = make_kqid(&init_user_ns, qid->type, entry->id); > > > > > +out_unlock: > > > > > + up_read(&dqopt->dqio_sem); > > > > > + return ret; > > > > > +} > > > > > + > > > > > +static const struct quota_format_ops mem_format_ops = { > > > > > + .check_quota_file = mem_check_quota_file, > > > > > + .read_file_info = mem_read_file_info, > > > > > + .write_file_info = mem_write_file_info, > > > > > + .free_file_info = mem_free_file_info, > > > > > + .read_dqblk = mem_read_dquot, > > > > > + .commit_dqblk = mem_write_dquot, > > > > > + .release_dqblk = mem_release_dquot, > > > > > + .get_next_id = mem_get_next_id, > > > > > +}; > > > > > + > > > > > +static struct quota_format_type mem_quota_format = { > > > > > + .qf_fmt_id = QFMT_MEM_ONLY, > > > > > + .qf_ops = &mem_format_ops, > > > > > + .qf_owner = THIS_MODULE > > > > > +}; > > > > > + > > > > > +static int __init init_mem_quota_format(void) > > > > > +{ > > > > > + return register_quota_format(&mem_quota_format); > > > > > +} > > > > > + > > > > > +static void __exit exit_mem_quota_format(void) > > > > > +{ > > > > > + unregister_quota_format(&mem_quota_format); > > > > > +} > > > > > + > > > > > +module_init(init_mem_quota_format); > > > > > +module_exit(exit_mem_quota_format); > > > > > diff --git a/include/linux/quota.h b/include/linux/quota.h > > > > > index fd692b4a41d5..4398e05c8b72 100644 > > > > > --- a/include/linux/quota.h > > > > > +++ b/include/linux/quota.h > > > > > @@ -285,7 +285,11 @@ static inline void dqstats_dec(unsigned int type) > > > > > #define DQ_FAKE_B 3 /* no limits only usage */ > > > > > #define DQ_READ_B 4 /* dquot was read into memory */ > > > > > #define DQ_ACTIVE_B 5 /* dquot is active (dquot_release not called) */ > > > > > -#define DQ_LASTSET_B 6 /* Following 6 bits (see QIF_) are reserved\ > > > > > +#define DQ_NO_SHRINK_B 6 /* modified dquot (not DQ_FAKE_B) is never to > > > > > + * be released by a shrinker. It should remain > > > > > + * in memory until quotas are being disabled on > > > > > + * unmount. */ > > > > > +#define DQ_LASTSET_B 7 /* Following 6 bits (see QIF_) are reserved\ > > > > > * for the mask of entries set via SETQUOTA\ > > > > > * quotactl. They are set under dq_data_lock\ > > > > > * and the quota format handling dquot can\ > > > > > @@ -536,6 +540,7 @@ struct quota_module_name { > > > > > {QFMT_VFS_OLD, "quota_v1"},\ > > > > > {QFMT_VFS_V0, "quota_v2"},\ > > > > > {QFMT_VFS_V1, "quota_v2"},\ > > > > > + {QFMT_MEM_ONLY, "quota_mem"},\ > > > > > {0, NULL}} > > > > > > > > > > #endif /* _QUOTA_ */ > > > > > diff --git a/include/uapi/linux/quota.h b/include/uapi/linux/quota.h > > > > > index f17c9636a859..ee9d2bad00c7 100644 > > > > > --- a/include/uapi/linux/quota.h > > > > > +++ b/include/uapi/linux/quota.h > > > > > @@ -77,6 +77,7 @@ > > > > > #define QFMT_VFS_V0 2 > > > > > #define QFMT_OCFS2 3 > > > > > #define QFMT_VFS_V1 4 > > > > > +#define QFMT_MEM_ONLY 5 > > > > > > > > > > /* Size of block in which space limits are passed through the quota > > > > > * interface */ > > > > > -- > > > > > 2.38.1 > > > > > > > > > > > > > > > > > >