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Wed, 20 Nov 2024 12:15:18 +0800 Message-ID: Date: Wed, 20 Nov 2024 12:15:18 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] vfs: support caching symlink lengths in inodes To: Mateusz Guzik , CC: , , , , , , , References: <20241119094555.660666-1-mjguzik@gmail.com> <20241119094555.660666-2-mjguzik@gmail.com> Content-Language: en-US From: "wangjianjian (C)" In-Reply-To: <20241119094555.660666-2-mjguzik@gmail.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.108.234.194] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemf200016.china.huawei.com (7.202.181.9) X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 931ED180010 X-Stat-Signature: ro45p9w5oi7afc16iajmtbgfdwb59gir X-HE-Tag: 1732076074-821312 X-HE-Meta: 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 XpgBWtk+ cyAYK0PJ5tAASICNXSkd/77pfKNH4Yr4wLKjJlW+QnklxzBmt3of2IIXJ9+7iJHrumSE4tNSLSqesNZfK47rjADvvsCIch9M5gWVpPkh34oYNXa9yisREhtlDtV6RAajxMJ3f0FqvCzxCjJG+sQoRmLUJMg3HFzSPPmxRn7mSAxQCgRdEPhsd9B6l6s5VGI9G24BI X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/11/19 17:45, Mateusz Guzik wrote: > When utilized it dodges strlen() in vfs_readlink(), giving about 1.5% > speed up when issuing readlink on /initrd.img on ext4. > > Filesystems opt in by calling inode_set_cached_link() when creating an > inode. > > The size is stored in what used to be a 4-byte hole. If necessary the > field can be made smaller and converted into a union with something not > used with symlinks. > > Churn-wise the current readlink_copy() helper is patched to accept the > size instead of calculating it. > > Signed-off-by: Mateusz Guzik > --- > fs/namei.c | 34 +++++++++++++++++++--------------- > fs/proc/namespaces.c | 2 +- > include/linux/fs.h | 12 ++++++++++-- > security/apparmor/apparmorfs.c | 2 +- > 4 files changed, 31 insertions(+), 19 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index 9d30c7aa9aa6..e56c29a22d26 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -5272,19 +5272,16 @@ SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newna > getname(newname), 0); > } > > -int readlink_copy(char __user *buffer, int buflen, const char *link) > +int readlink_copy(char __user *buffer, int buflen, const char *link, int linklen) > { > - int len = PTR_ERR(link); > - if (IS_ERR(link)) > - goto out; > + int copylen; > > - len = strlen(link); > - if (len > (unsigned) buflen) > - len = buflen; > - if (copy_to_user(buffer, link, len)) > - len = -EFAULT; > -out: > - return len; > + copylen = linklen; > + if (unlikely(copylen > (unsigned) buflen)) > + copylen = buflen; > + if (copy_to_user(buffer, link, copylen)) > + copylen = -EFAULT; > + return copylen; > } > > /** > @@ -5304,6 +5301,9 @@ int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen) > const char *link; > int res; > > + if (inode->i_opflags & IOP_CACHED_LINK) > + return readlink_copy(buffer, buflen, inode->i_link, inode->i_linklen); > + > if (unlikely(!(inode->i_opflags & IOP_DEFAULT_READLINK))) { > if (unlikely(inode->i_op->readlink)) > return inode->i_op->readlink(dentry, buffer, buflen); > @@ -5322,7 +5322,7 @@ int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen) > if (IS_ERR(link)) > return PTR_ERR(link); > } > - res = readlink_copy(buffer, buflen, link); > + res = readlink_copy(buffer, buflen, link, strlen(link)); > do_delayed_call(&done); > return res; > } > @@ -5391,10 +5391,14 @@ EXPORT_SYMBOL(page_put_link); > > int page_readlink(struct dentry *dentry, char __user *buffer, int buflen) > { > + const char *link; > + int res; > + > DEFINE_DELAYED_CALL(done); > - int res = readlink_copy(buffer, buflen, > - page_get_link(dentry, d_inode(dentry), > - &done)); > + link = page_get_link(dentry, d_inode(dentry), &done); > + res = PTR_ERR(link); > + if (!IS_ERR(link)) > + res = readlink_copy(buffer, buflen, link, strlen(link)); > do_delayed_call(&done); > return res; > } > diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c > index 8e159fc78c0a..c610224faf10 100644 > --- a/fs/proc/namespaces.c > +++ b/fs/proc/namespaces.c > @@ -83,7 +83,7 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl > if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { > res = ns_get_name(name, sizeof(name), task, ns_ops); > if (res >= 0) > - res = readlink_copy(buffer, buflen, name); > + res = readlink_copy(buffer, buflen, name, strlen(name)); > } > put_task_struct(task); > return res; > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 972147da71f9..30e332fb399d 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -626,6 +626,7 @@ is_uncached_acl(struct posix_acl *acl) > #define IOP_XATTR 0x0008 > #define IOP_DEFAULT_READLINK 0x0010 > #define IOP_MGTIME 0x0020 > +#define IOP_CACHED_LINK 0x0040 > > /* > * Keep mostly read-only and often accessed (especially for > @@ -686,7 +687,7 @@ struct inode { > > /* Misc */ > u32 i_state; > - /* 32-bit hole */ > + int i_linklen; /* for symlinks */ > struct rw_semaphore i_rwsem; > > unsigned long dirtied_when; /* jiffies of first dirtying */ > @@ -749,6 +750,13 @@ struct inode { > void *i_private; /* fs or device private pointer */ > } __randomize_layout; > > +static inline void inode_set_cached_link(struct inode *inode, char *link, int linklen) > +{ > + inode->i_link = link; > + inode->i_linklen = linklen; Just curious, is this linklen equal to inode size? if it is, why don't use it? > + inode->i_opflags |= IOP_CACHED_LINK; > +} > + > /* > * Get bit address from inode->i_state to use with wait_var_event() > * infrastructre. > @@ -3351,7 +3359,7 @@ extern const struct file_operations generic_ro_fops; > > #define special_file(m) (S_ISCHR(m)||S_ISBLK(m)||S_ISFIFO(m)||S_ISSOCK(m)) > > -extern int readlink_copy(char __user *, int, const char *); > +extern int readlink_copy(char __user *, int, const char *, int); > extern int page_readlink(struct dentry *, char __user *, int); > extern const char *page_get_link(struct dentry *, struct inode *, > struct delayed_call *); > diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c > index 01b923d97a44..60959cfba672 100644 > --- a/security/apparmor/apparmorfs.c > +++ b/security/apparmor/apparmorfs.c > @@ -2611,7 +2611,7 @@ static int policy_readlink(struct dentry *dentry, char __user *buffer, > res = snprintf(name, sizeof(name), "%s:[%lu]", AAFS_NAME, > d_inode(dentry)->i_ino); > if (res > 0 && res < sizeof(name)) > - res = readlink_copy(buffer, buflen, name); > + res = readlink_copy(buffer, buflen, name, strlen(name)); > else > res = -ENOENT; > -- Regards