Re: [PATCH] alloc_tag: avoid mem alloc and iter reset when reading allocinfo

Suren Baghdasaryan
2025-05-07T23:36:29Z

On Wed, May 7, 2025 at 5:55 PM David Wang <00107082@163.com> wrote:
>
> ---
> The patch is not complete, just want to get feedbacks whether this
> worth carrying on.

In such cases it's customary to mark the patch as RFC which saves you
time on explaining your motivation :)

> ---
> When reading /proc/allocinfo, for each read syscall, seq_file would
> invoke start/stop callbacks. In start callback, a memory is alloced
> to store iterator and the iterator would restart from beginning to
> walk to its previous position.
> Each seq_file read() takes at most 4096 bytes, even read with a larger
> user space buffer, meaning read out /proc/allocinfo, tens of read
> syscalls are needed. For example, a 306036 bytes allocinfo files need
> 76 reads:
>
> $ sudo cat /proc/allocinfo | wc
> 3964 16678 306036
>
> For those n=3964 lines, each read takes about m=3964/76=52 lines,
> the iter would be rewinding:
> m steps on 1st read,
> 2*m steps on 2nd read
> 3*m steps on 3rd read
> ...
> n steps on the last read
> totally, the iterator would be iterated O(n*n/m) times.
> (Each read would take more time than previous one.)
>
> To use a private data alloced when /proc/allocinfo is opened,
> the n/m memory alloction could be avoid, and there is no need
> to restart the iterator from very beginning everytime.
> So only 1 memory allocation and n steps for iterating are needed.
> (Only when module changed, the iterator should be invalidated and
> restart.)

Yeah, your change makes sense and looks like a good optimization. From
a quick look at the code, codetag_next_ct() should handle the case
when a module gets removed from under us while we are not holding
cttype->mod_lock. I'll need to take another closer look at it once you
post an official patch.
Thanks!

>
> Timings before:
> $ time cat /proc/allocinfo > /dev/null
>
> real 0m0.007s
> user 0m0.000s
> sys 0m0.007s
> read-syscalls get slower and slower:
> read(3, "allocinfo - version: 1.0\n# <"..., 131072) = 4085 <0.000062>
> ...
> read(3, " 0 0 drivers/gp"..., 131072) = 4046 <0.000135>
> read(3, " 0 0 sound/core"..., 131072) = 4021 <0.000150>
> ...
>
> and with the change:
> $ time cat /proc/allocinfo > /dev/null
>
> real 0m0.004s
> user 0m0.000s
> sys 0m0.003s
> 7ms drop to 4ms, more friendly to monitoring tools.
>
> Detailed strace stats before the change:
> $ sudo strace -T -e read cat /proc/allocinfo > /dev/null
> read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@>\2\0\0\0\0\0"..., 832) = 832 <0.000040>
> read(3, "allocinfo - version: 1.0\n# <"..., 131072) = 4085 <0.000062>
> read(3, " 4096 1 arch/x86/k"..., 131072) = 4063 <0.000062>
> read(3, " 0 0 arch/x86/k"..., 131072) = 4029 <0.000061>
> read(3, " 64 1 kernel/wor"..., 131072) = 4064 <0.000061>
> read(3, " 0 0 kernel/sch"..., 131072) = 4041 <0.000051>
> read(3, " 4992 39 kernel/irq"..., 131072) = 4061 <0.000070>
> read(3, " 0 0 kernel/fut"..., 131072) = 4060 <0.000071>
> read(3, " 0 0 kernel/aud"..., 131072) = 4025 <0.000122>
> read(3, " 1536 3 kernel/tra"..., 131072) = 4014 <0.000064>
> read(3, " 0 0 kernel/tra"..., 131072) = 4079 <0.000067>
> read(3, " 0 0 kernel/tra"..., 131072) = 4035 <0.000072>
> read(3, " 0 0 kernel/bpf"..., 131072) = 4044 <0.000074>
> read(3, " 0 0 kernel/bpf"..., 131072) = 4061 <0.000063>
> read(3, " 0 0 ./include/"..., 131072) = 4084 <0.000063>
> read(3, " 0 0 kernel/eve"..., 131072) = 4084 <0.000071>
> read(3, " 278528 68 mm/memory."..., 131072) = 4068 <0.000070>
> read(3, " 0 0 mm/zswap.c"..., 131072) = 4091 <0.000082>
> read(3, " 0 0 mm/balloon"..., 131072) = 4039 <0.000083>
> read(3, " 0 0 fs/splice."..., 131072) = 4095 <0.000083>
> read(3, " 0 0 fs/binfmt_"..., 131072) = 4039 <0.000075>
> read(3, " 192 3 fs/proc/kc"..., 131072) = 4088 <0.000076>
> read(3, " 0 0 ipc/mqueue"..., 131072) = 4017 <0.000076>
> read(3, " 0 0 security/s"..., 131072) = 4075 <0.000072>
> read(3, " 0 0 security/s"..., 131072) = 4029 <0.000084>
> read(3, " 0 0 security/t"..., 131072) = 4053 <0.000076>
> read(3, " 0 0 security/a"..., 131072) = 4054 <0.000078>
> read(3, " 0 0 crypto/rsa"..., 131072) = 4046 <0.000081>
> read(3, " 0 0 crypto/asy"..., 131072) = 4079 <0.000081>
> read(3, " 1728 9 block/blk-"..., 131072) = 4034 <0.000084>
> read(3, " 0 0 io_uring/r"..., 131072) = 4044 <0.000085>
> read(3, " 0 0 lib/crypto"..., 131072) = 4056 <0.000363>
> read(3, " 0 0 lib/pldmfw"..., 131072) = 4079 <0.000091>
> read(3, " 384 6 drivers/pc"..., 131072) = 4091 <0.000098>
> read(3, " 0 0 drivers/vi"..., 131072) = 4068 <0.000093>
> read(3, " 4096 1 drivers/ac"..., 131072) = 4086 <0.000089>
> read(3, " 11040 230 drivers/ac"..., 131072) = 4001 <0.000090>
> read(3, " 0 0 drivers/ac"..., 131072) = 4030 <0.000094>
> read(3, " 0 0 drivers/dm"..., 131072) = 4031 <0.000094>
> read(3, " 0 0 drivers/xe"..., 131072) = 4085 <0.000097>
> read(3, " 4224 33 drivers/tt"..., 131072) = 4086 <0.000097>
> read(3, " 0 0 drivers/io"..., 131072) = 4038 <0.000097>
> read(3, " 0 0 drivers/io"..., 131072) = 4034 <0.000100>
> read(3, " 64 2 drivers/ba"..., 131072) = 4094 <0.000110>
> read(3, " 0 0 drivers/ba"..., 131072) = 4025 <0.000100>
> read(3, " 0 0 drivers/dm"..., 131072) = 4077 <0.000106>
> read(3, " 0 0 drivers/i2"..., 131072) = 4049 <0.000103>
> read(3, " 0 0 drivers/ed"..., 131072) = 4035 <0.000108>
> read(3, " 0 0 drivers/fi"..., 131072) = 4052 <0.000107>
> read(3, " 0 0 net/core/s"..., 131072) = 4057 <0.000119>
> read(3, " 5248 82 net/core/r"..., 131072) = 4050 <0.000110>
> read(3, " 0 0 net/core/d"..., 131072) = 4047 <0.000111>
> read(3, " 0 0 net/ethtoo"..., 131072) = 4059 <0.000112>
> read(3, " 32 1 net/ipv4/r"..., 131072) = 4052 <0.000116>
> read(3, " 1920 10 net/ipv4/i"..., 131072) = 4040 <0.000116>
> read(3, " 0 0 net/xfrm/x"..., 131072) = 4071 <0.000118>
> read(3, " 0 0 net/ipv6/i"..., 131072) = 4053 <0.000120>
> read(3, " 0 0 net/devlin"..., 131072) = 4064 <0.000120>
> read(3, " 0 0 lib/decomp"..., 131072) = 3996 <0.000123>
> read(3, " 0 0 drivers/vi"..., 131072) = 4043 <0.000121>
> read(3, " 0 0 drivers/us"..., 131072) = 4045 <0.000123>
> read(3, " 0 0 drivers/us"..., 131072) = 4020 <0.000126>
> read(3, " 64 1 drivers/sc"..., 131072) = 4043 <0.000128>
> read(3, " 0 0 drivers/ne"..., 131072) = 4094 <0.000130>
> read(3, " 0 0 drivers/hi"..., 131072) = 4025 <0.000132>
> read(3, " 672 6 fs/ext4/mb"..., 131072) = 4071 <0.000132>
> read(3, " 0 0 fs/autofs/"..., 131072) = 4038 <0.000134>
> read(3, " 0 0 fs/fuse/fi"..., 131072) = 4093 <0.000134>
> read(3, " 0 0 drivers/gp"..., 131072) = 4035 <0.000133>
> read(3, " 0 0 drivers/gp"..., 131072) = 4046 <0.000135>
> read(3, " 0 0 sound/core"..., 131072) = 4021 <0.000150>
> read(3, " 0 0 sound/core"..., 131072) = 4000 <0.000134>
> read(3, " 2048 1 drivers/vi"..., 131072) = 4078 <0.000138>
> read(3, " 3328 104 drivers/gp"..., 131072) = 4040 <0.000143>
> read(3, " 0 0 fs/overlay"..., 131072) = 4075 <0.000141>
> read(3, " 0 0 net/netfil"..., 131072) = 4061 <0.000139>
> read(3, " 0 0 net/xfrm/x"..., 131072) = 2022 <0.000129>
> read(3, "", 131072) = 0 <0.000114>
>
> And with this change:
> $ sudo strace -T -e read cat /proc/allocinfo > /dev/null
> read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@>\2\0\0\0\0\0"..., 832) = 832 <0.000018>
> read(3, "allocinfo - version: 1.0\n# <"..., 131072) = 4085 <0.000066>
> read(3, " 4096 1 arch/x86/k"..., 131072) = 4063 <0.000062>
> read(3, " 0 0 arch/x86/k"..., 131072) = 4029 <0.000062>
> read(3, " 64 1 kernel/wor"..., 131072) = 4064 <0.000064>
> read(3, " 0 0 kernel/sch"..., 131072) = 4041 <0.000046>
> read(3, " 4992 39 kernel/irq"..., 131072) = 4061 <0.000053>
> read(3, " 0 0 kernel/fut"..., 131072) = 4060 <0.000054>
> read(3, " 0 0 kernel/aud"..., 131072) = 4025 <0.000053>
> read(3, " 1536 3 kernel/tra"..., 131072) = 4014 <0.000051>
> read(3, " 0 0 kernel/tra"..., 131072) = 4079 <0.000050>
> read(3, " 0 0 kernel/tra"..., 131072) = 4035 <0.000051>
> read(3, " 0 0 kernel/bpf"..., 131072) = 4044 <0.000053>
> read(3, " 0 0 kernel/bpf"..., 131072) = 4061 <0.000053>
> read(3, " 0 0 ./include/"..., 131072) = 4084 <0.000052>
> read(3, " 0 0 kernel/eve"..., 131072) = 4084 <0.000072>
> read(3, " 286720 70 mm/memory."..., 131072) = 4068 <0.000071>
> read(3, " 0 0 mm/zswap.c"..., 131072) = 4091 <0.000056>
> read(3, " 0 0 mm/balloon"..., 131072) = 4039 <0.000056>
> read(3, " 0 0 fs/splice."..., 131072) = 4095 <0.000076>
> read(3, " 0 0 fs/binfmt_"..., 131072) = 4039 <0.000075>
> read(3, " 192 3 fs/proc/kc"..., 131072) = 4088 <0.000057>
> read(3, " 0 0 ipc/mqueue"..., 131072) = 4017 <0.000055>
> read(3, " 0 0 security/s"..., 131072) = 4075 <0.000046>
> read(3, " 0 0 security/s"..., 131072) = 4029 <0.000045>
> read(3, " 0 0 security/t"..., 131072) = 4053 <0.000050>
> read(3, " 0 0 security/a"..., 131072) = 4054 <0.000060>
> read(3, " 0 0 crypto/rsa"..., 131072) = 4046 <0.000181>
> read(3, " 0 0 crypto/asy"..., 131072) = 4079 <0.000051>
> read(3, " 1728 9 block/blk-"..., 131072) = 4034 <0.000070>
> read(3, " 0 0 io_uring/r"..., 131072) = 4044 <0.000078>
> read(3, " 0 0 lib/crypto"..., 131072) = 4066 <0.000067>
> read(3, " 0 0 arch/x86/l"..., 131072) = 4085 <0.000066>
> read(3, " 7168 7 drivers/pc"..., 131072) = 4090 <0.000066>
> read(3, " 0 0 drivers/vi"..., 131072) = 4063 <0.000065>
> read(3, " 1024 1 drivers/ac"..., 131072) = 4094 <0.000067>
> read(3, " 0 0 drivers/ac"..., 131072) = 4023 <0.000063>
> read(3, " 2048 2 drivers/ac"..., 131072) = 4020 <0.000066>
> read(3, " 0 0 drivers/dm"..., 131072) = 4094 <0.000067>
> read(3, " 0 0 drivers/xe"..., 131072) = 4087 <0.000068>
> read(3, " 1024 1 drivers/tt"..., 131072) = 4093 <0.000056>
> read(3, " 0 0 drivers/io"..., 131072) = 4037 <0.000044>
> read(3, " 0 0 drivers/io"..., 131072) = 4095 <0.000061>
> read(3, " 0 0 drivers/ba"..., 131072) = 4045 <0.000059>
> read(3, " 0 0 drivers/ba"..., 131072) = 4011 <0.000057>
> read(3, " 0 0 drivers/ma"..., 131072) = 4087 <0.000064>
> read(3, " 0 0 drivers/i2"..., 131072) = 4028 <0.000059>
> read(3, " 0 0 drivers/ed"..., 131072) = 4048 <0.000080>
> read(3, " 0 0 drivers/fi"..., 131072) = 4082 <0.000054>
> read(3, " 0 0 net/core/s"..., 131072) = 4091 <0.000068>
> read(3, " 0 0 net/core/f"..., 131072) = 4041 <0.000053>
> read(3, " 20 1 net/sched/"..., 131072) = 4054 <0.000051>
> read(3, " 0 0 net/ethtoo"..., 131072) = 4045 <0.000051>
> read(3, " 0 0 net/ipv4/r"..., 131072) = 4040 <0.000051>
> read(3, " 2048 1 net/ipv4/f"..., 131072) = 4056 <0.000050>
> read(3, " 0 0 net/xfrm/x"..., 131072) = 4053 <0.000056>
> read(3, " 3072 6 net/ipv6/i"..., 131072) = 4095 <0.000060>
> read(3, " 0 0 net/devlin"..., 131072) = 4094 <0.000064>
> read(3, " 0 0 lib/decomp"..., 131072) = 4023 <0.000063>
> read(3, " 2048 2 drivers/us"..., 131072) = 4053 <0.000062>
> read(3, " 0 0 drivers/us"..., 131072) = 4011 <0.000068>
> read(3, " 0 0 drivers/in"..., 131072) = 4092 <0.000059>
> read(3, " 64 1 drivers/sc"..., 131072) = 4067 <0.000064>
> read(3, " 0 0 drivers/ne"..., 131072) = 4059 <0.000067>
> read(3, " 8 1 drivers/hi"..., 131072) = 4050 <0.000052>
> read(3, " 256 1 fs/ext4/mb"..., 131072) = 4024 <0.000070>
> read(3, " 0 0 fs/autofs/"..., 131072) = 4082 <0.000070>
> read(3, " 0 0 fs/fuse/in"..., 131072) = 4074 <0.000054>
> read(3, " 0 0 drivers/gp"..., 131072) = 4066 <0.000063>
> read(3, " 0 0 drivers/gp"..., 131072) = 4091 <0.000052>
> read(3, " 0 0 drivers/gp"..., 131072) = 4029 <0.000064>
> read(3, " 0 0 drivers/gp"..., 131072) = 4094 <0.000062>
> read(3, " 128 2 sound/core"..., 131072) = 4069 <0.000068>
> read(3, " 64 1 sound/pci/"..., 131072) = 4074 <0.000069>
> read(3, " 384 4 net/bridge"..., 131072) = 4021 <0.000054>
> read(3, " 0 0 net/netfil"..., 131072) = 4084 <0.000050>
> read(3, " 0 0 net/xfrm/x"..., 131072) = 1513 <0.000047>
> read(3, "", 131072) = 0 <0.000030>
>
> Signed-off-by: David Wang <00107082@163.com>
> ---
> lib/alloc_tag.c | 30 +++++++++++-------------------
> 1 file changed, 11 insertions(+), 19 deletions(-)
>
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index 25ecc1334b67..ec83cf798209 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -45,21 +45,17 @@ struct allocinfo_private {
> static void *allocinfo_start(struct seq_file *m, loff_t *pos)
> {
> struct allocinfo_private *priv;
> - struct codetag *ct;
> loff_t node = *pos;
>
> - priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> - m->private = priv;
> - if (!priv)
> - return NULL;
> -
> - priv->print_header = (node == 0);
> + priv = (struct allocinfo_private *)m->private;
> codetag_lock_module_list(alloc_tag_cttype, true);
> - priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> - while ((ct = codetag_next_ct(&priv->iter)) != NULL && node)
> - node--;
> -
> - return ct ? priv : NULL;
> + if (node == 0) {
> + priv->print_header = true;
> + priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> + codetag_next_ct(&priv->iter);
> + }
> + // TODO: need to check iter is valid, or rewinding it.
> + return priv->iter.ct ? priv : NULL;
> }
>
> static void *allocinfo_next(struct seq_file *m, void *arg, loff_t *pos)
> @@ -76,12 +72,7 @@ static void *allocinfo_next(struct seq_file *m, void *arg, loff_t *pos)
>
> static void allocinfo_stop(struct seq_file *m, void *arg)
> {
> - struct allocinfo_private *priv = (struct allocinfo_private *)m->private;
> -
> - if (priv) {
> - codetag_lock_module_list(alloc_tag_cttype, false);
> - kfree(priv);
> - }
> + codetag_lock_module_list(alloc_tag_cttype, false);
> }
>
> static void print_allocinfo_header(struct seq_buf *buf)
> @@ -249,7 +240,8 @@ static void __init procfs_init(void)
> if (!mem_profiling_support)
> return;
>
> - if (!proc_create_seq(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_seq_op)) {
> + if (!proc_create_seq_private(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_seq_op,
> + sizeof(struct allocinfo_private), NULL)) {
> pr_err("Failed to create %s file\n", ALLOCINFO_FILE_NAME);
> shutdown_mem_profiling(false);
> }
> --
> 2.39.2
>