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Message-ID: <55a00d7f-bb9d-b59b-9af6-db7f2601c453@linux.alibaba.com>
Date: Thu, 15 Sep 2022 11:27:19 +0800
From: JeffleXu <jefflexu@...ux.alibaba.com>
To: Jia Zhu <zhujia.zj@...edance.com>, linux-erofs@...ts.ozlabs.org,
xiang@...nel.org, chao@...nel.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
yinxin.x@...edance.com, huyue2@...lpad.com
Subject: Re: [PATCH V3 4/6] erofs: introduce fscache-based domain
On 9/14/22 6:50 PM, Jia Zhu wrote:
> A new fscache-based shared domain mode is going to be introduced for
> erofs. In which case, same data blobs in same domain will be shared
> and reused to reduce on-disk space usage.
>
> As the first step, we use pseudo mnt to manage and maintain domain's
> lifecycle.
The commit message needs to be updated, since the pseudo mnt is not
introduced yet in this patch.
>
> The implementation of sharing blobs will be introduced in subsequent
> patches.
>
> Signed-off-by: Jia Zhu <zhujia.zj@...edance.com>
> ---
> fs/erofs/fscache.c | 134 ++++++++++++++++++++++++++++++++++++++------
> fs/erofs/internal.h | 9 +++
> 2 files changed, 127 insertions(+), 16 deletions(-)
>
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 4159cf781924..b2100dc67cde 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -1,10 +1,14 @@
> // SPDX-License-Identifier: GPL-2.0-or-later
> /*
> * Copyright (C) 2022, Alibaba Cloud
> + * Copyright (C) 2022, Bytedance Inc. All rights reserved.
> */
> #include <linux/fscache.h>
> #include "internal.h"
>
> +static DEFINE_MUTEX(erofs_domain_list_lock);
> +static LIST_HEAD(erofs_domain_list);
> +
> static struct netfs_io_request *erofs_fscache_alloc_request(struct address_space *mapping,
> loff_t start, size_t len)
> {
> @@ -417,6 +421,106 @@ const struct address_space_operations erofs_fscache_access_aops = {
> .readahead = erofs_fscache_readahead,
> };
>
> +static
> +struct erofs_domain *erofs_fscache_domain_get(struct erofs_domain *domain)
> +{
> + refcount_inc(&domain->ref);
refcount_inc_not_zero() is prefered here.
Considering the following time sequence:
CPU1 CPU2
------ ------
erofs_fscache_domain_put
refcount decreased to 0
erofs_fscache_register_domain
mutex_lock
erofs_fscache_domain_get
inc refcount to 1
mutex_unlock
mutex_lock
remove the domain from list
mutex_unlock
> + return domain;
> +}
> +
> +static void erofs_fscache_domain_put(struct erofs_domain *domain)
> +{
> + if (!domain)
> + return;
> + if (refcount_dec_and_test(&domain->ref)) {
> + fscache_relinquish_volume(domain->volume, NULL, false);
> + mutex_lock(&erofs_domain_list_lock);
> + list_del(&domain->list);
> + mutex_unlock(&erofs_domain_list_lock);
We need to delete the domain from the list first, and then calling
fscache_relinquish_volume(), so that others won't race with this.
> + kfree(domain->domain_id);
> + kfree(domain);
> + }
> +}
> +
> +static int erofs_fscache_register_volume(struct super_block *sb)
> +{
> + struct erofs_sb_info *sbi = EROFS_SB(sb);
> + char *domain_id = sbi->opt.domain_id;
> + struct fscache_volume *volume;
> + char *name;
> + int ret = 0;
> +
> + if (domain_id)
> + name = kasprintf(GFP_KERNEL, "erofs,%s", domain_id);
> + else
> + name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
> + if (!name)
> + return -ENOMEM;
> +
> + volume = fscache_acquire_volume(name, NULL, NULL, 0);
> + if (IS_ERR_OR_NULL(volume)) {
> + erofs_err(sb, "failed to register volume for %s", name);
> + ret = volume ? PTR_ERR(volume) : -EOPNOTSUPP;
> + volume = NULL;
> + }
> +
> + sbi->volume = volume;
> + kfree(name);
> + return ret;
> +}
> +
> +static int erofs_fscache_init_domain(struct super_block *sb)
> +{
> + int err;
> + struct erofs_domain *domain;
> + struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> + domain = kzalloc(sizeof(struct erofs_domain), GFP_KERNEL);
> + if (!domain)
> + return -ENOMEM;
> +
> + domain->domain_id = kstrdup(sbi->opt.domain_id, GFP_KERNEL);
> + if (!domain->domain_id) {
> + kfree(domain);
> + return -ENOMEM;
> + }
> + sbi->domain = domain;
Why bothering setting sbi->domain here? Can't we set sbi->domain finnaly
when the domain has been fully initialized?
> + err = erofs_fscache_register_volume(sb);
> + if (err)
> + goto out;
> +
> + domain->volume = sbi->volume;
> + refcount_set(&domain->ref, 1);
> + mutex_init(&domain->mutex);
> + list_add(&domain->list, &erofs_domain_list);
> + return 0;
> +out:
> + kfree(domain->domain_id);
> + kfree(domain);
> + sbi->domain = NULL;
> + return err;
> +}
> +
> +static int erofs_fscache_register_domain(struct super_block *sb)
> +{
> + int err;
> + struct erofs_domain *domain;
> + struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> + mutex_lock(&erofs_domain_list_lock);
> + list_for_each_entry(domain, &erofs_domain_list, list) {
> + if (!strcmp(domain->domain_id, sbi->opt.domain_id)) {
> + sbi->domain = erofs_fscache_domain_get(domain);
> + sbi->volume = domain->volume;
> + mutex_unlock(&erofs_domain_list_lock);
> + return 0;
> + }
> + }
> + err = erofs_fscache_init_domain(sb);
> + mutex_unlock(&erofs_domain_list_lock);
> + return err;
> +}
> +
> struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
> char *name, bool need_inode)
> {
> @@ -486,24 +590,16 @@ void erofs_fscache_unregister_cookie(struct erofs_fscache *ctx)
> int erofs_fscache_register_fs(struct super_block *sb)
> {
> struct erofs_sb_info *sbi = EROFS_SB(sb);
> - struct fscache_volume *volume;
> struct erofs_fscache *fscache;
> - char *name;
> - int ret = 0;
> + int ret;
>
> - name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
> - if (!name)
> - return -ENOMEM;
> + if (sbi->opt.domain_id)
> + ret = erofs_fscache_register_domain(sb);
> + else
> + ret = erofs_fscache_register_volume(sb);
>
> - volume = fscache_acquire_volume(name, NULL, NULL, 0);
> - if (IS_ERR_OR_NULL(volume)) {
> - erofs_err(sb, "failed to register volume for %s", name);
> - ret = volume ? PTR_ERR(volume) : -EOPNOTSUPP;
> - volume = NULL;
> - }
> -
> - sbi->volume = volume;
> - kfree(name);
> + if (ret)
> + return ret;
>
> fscache = erofs_fscache_register_cookie(sb, sbi->opt.fsid, true);
> if (IS_ERR(fscache))
> @@ -518,7 +614,13 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
> struct erofs_sb_info *sbi = EROFS_SB(sb);
>
> erofs_fscache_unregister_cookie(sbi->s_fscache);
> - fscache_relinquish_volume(sbi->volume, NULL, false);
> sbi->s_fscache = NULL;
> +
> + if (sbi->domain)
> + erofs_fscache_domain_put(sbi->domain);
> + else
> + fscache_relinquish_volume(sbi->volume, NULL, false);
> +
> sbi->volume = NULL;
> + sbi->domain = NULL;
> }
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 2d129c6b3027..5ce6889d6f1d 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -99,6 +99,14 @@ struct erofs_sb_lz4_info {
> u16 max_pclusterblks;
> };
>
> +struct erofs_domain {
> + refcount_t ref;
> + struct mutex mutex;
> + struct list_head list;
> + struct fscache_volume *volume;
> + char *domain_id;
> +};
> +
> struct erofs_fscache {
> struct fscache_cookie *cookie;
> struct inode *inode;
> @@ -158,6 +166,7 @@ struct erofs_sb_info {
> /* fscache support */
> struct fscache_volume *volume;
> struct erofs_fscache *s_fscache;
> + struct erofs_domain *domain;
> };
>
> #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
--
Thanks,
Jingbo
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