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Date: Mon, 24 Jun 2024 08:25:29 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: alexjlzheng@...il.com
Cc: chandan.babu@...cle.com, linux-xfs@...r.kernel.org,
linux-kernel@...r.kernel.org, alexjlzheng@...cent.com
Subject: Re: [PATCH] xfs: make xfs_log_iovec independent from xfs_log_vec and
release it early
On Sun, Jun 23, 2024 at 08:31:19PM +0800, alexjlzheng@...il.com wrote:
> From: Jinliang Zheng <alexjlzheng@...cent.com>
>
> In the current implementation, in most cases, the memory of xfs_log_vec
> and xfs_log_iovec is allocated together. Therefore the life cycle of
> xfs_log_iovec has to remain the same as xfs_log_vec.
>
> But this is not necessary. When the content in xfs_log_iovec is written
> to iclog by xlog_write(), it no longer needs to exist in the memory. But
> xfs_log_vec is still useful, because after we flush the iclog into the
> disk log space, we need to find the corresponding xfs_log_item through
> the xfs_log_vec->lv_item field and add it to AIL.
>
> This patch separates the memory allocation of xfs_log_iovec from
> xfs_log_vec, and releases the memory of xfs_log_iovec in advance after
> the content in xfs_log_iovec is written to iclog.
Why would anyone care? This makes lifecycle reasoning more complicated
but no justification is provided.
--D
> Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
> ---
> fs/xfs/xfs_log.c | 2 ++
> fs/xfs/xfs_log.h | 8 ++++++--
> fs/xfs/xfs_log_cil.c | 26 ++++++++++++++++----------
> 3 files changed, 24 insertions(+), 12 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 416c15494983..f7af9550c17b 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2526,6 +2526,8 @@ xlog_write(
> xlog_write_full(lv, ticket, iclog, &log_offset,
> &len, &record_cnt, &data_cnt);
> }
> + if (lv->lv_flags & XFS_LOG_VEC_DYNAMIC)
> + kvfree(lv->lv_iovecp);
> }
> ASSERT(len == 0);
>
> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
> index d69acf881153..f052c7fdb3e9 100644
> --- a/fs/xfs/xfs_log.h
> +++ b/fs/xfs/xfs_log.h
> @@ -6,6 +6,8 @@
> #ifndef __XFS_LOG_H__
> #define __XFS_LOG_H__
>
> +#define XFS_LOG_VEC_DYNAMIC (1 << 0)
> +
> struct xfs_cil_ctx;
>
> struct xfs_log_vec {
> @@ -17,7 +19,8 @@ struct xfs_log_vec {
> char *lv_buf; /* formatted buffer */
> int lv_bytes; /* accounted space in buffer */
> int lv_buf_len; /* aligned size of buffer */
> - int lv_size; /* size of allocated lv */
> + int lv_size; /* size of allocated iovec + buffer */
> + int lv_flags; /* lv flags */
> };
>
> #define XFS_LOG_VEC_ORDERED (-1)
> @@ -40,6 +43,7 @@ static inline void
> xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec,
> int data_len)
> {
> + struct xfs_log_iovec *lvec = lv->lv_iovecp;
> struct xlog_op_header *oph = vec->i_addr;
> int len;
>
> @@ -69,7 +73,7 @@ xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec,
> vec->i_len = len;
>
> /* Catch buffer overruns */
> - ASSERT((void *)lv->lv_buf + lv->lv_bytes <= (void *)lv + lv->lv_size);
> + ASSERT((void *)lv->lv_buf + lv->lv_bytes <= (void *)lvec + lv->lv_size);
> }
>
> /*
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index f51cbc6405c1..3be9f86ce655 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -219,8 +219,7 @@ static inline int
> xlog_cil_iovec_space(
> uint niovecs)
> {
> - return round_up((sizeof(struct xfs_log_vec) +
> - niovecs * sizeof(struct xfs_log_iovec)),
> + return round_up(niovecs * sizeof(struct xfs_log_iovec),
> sizeof(uint64_t));
> }
>
> @@ -279,6 +278,7 @@ xlog_cil_alloc_shadow_bufs(
>
> list_for_each_entry(lip, &tp->t_items, li_trans) {
> struct xfs_log_vec *lv;
> + struct xfs_log_iovec *lvec;
> int niovecs = 0;
> int nbytes = 0;
> int buf_size;
> @@ -339,18 +339,23 @@ xlog_cil_alloc_shadow_bufs(
> * the buffer, only the log vector header and the iovec
> * storage.
> */
> - kvfree(lip->li_lv_shadow);
> - lv = xlog_kvmalloc(buf_size);
> -
> - memset(lv, 0, xlog_cil_iovec_space(niovecs));
> + if (lip->li_lv_shadow) {
> + kvfree(lip->li_lv_shadow->lv_iovecp);
> + kvfree(lip->li_lv_shadow);
> + }
> + lv = xlog_kvmalloc(sizeof(struct xfs_log_vec));
> + memset(lv, 0, sizeof(struct xfs_log_vec));
> + lvec = xlog_kvmalloc(buf_size);
> + memset(lvec, 0, xlog_cil_iovec_space(niovecs));
>
> + lv->lv_flags |= XFS_LOG_VEC_DYNAMIC;
> INIT_LIST_HEAD(&lv->lv_list);
> lv->lv_item = lip;
> lv->lv_size = buf_size;
> if (ordered)
> lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
> else
> - lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
> + lv->lv_iovecp = lvec;
> lip->li_lv_shadow = lv;
> } else {
> /* same or smaller, optimise common overwrite case */
> @@ -366,9 +371,9 @@ xlog_cil_alloc_shadow_bufs(
> lv->lv_niovecs = niovecs;
>
> /* The allocated data region lies beyond the iovec region */
> - lv->lv_buf = (char *)lv + xlog_cil_iovec_space(niovecs);
> + lv->lv_buf = (char *)lv->lv_iovecp +
> + xlog_cil_iovec_space(niovecs);
> }
> -
> }
>
> /*
> @@ -502,7 +507,7 @@ xlog_cil_insert_format_items(
> /* reset the lv buffer information for new formatting */
> lv->lv_buf_len = 0;
> lv->lv_bytes = 0;
> - lv->lv_buf = (char *)lv +
> + lv->lv_buf = (char *)lv->lv_iovecp +
> xlog_cil_iovec_space(lv->lv_niovecs);
> } else {
> /* switch to shadow buffer! */
> @@ -1544,6 +1549,7 @@ xlog_cil_process_intents(
> set_bit(XFS_LI_WHITEOUT, &ilip->li_flags);
> trace_xfs_cil_whiteout_mark(ilip);
> len += ilip->li_lv->lv_bytes;
> + kvfree(ilip->li_lv->lv_iovecp);
> kvfree(ilip->li_lv);
> ilip->li_lv = NULL;
>
> --
> 2.39.3
>
>
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