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Date: Tue, 25 Jun 2024 00:06:14 +0800
From: Jinliang Zheng <alexjlzheng@...il.com>
To: djwong@...nel.org
Cc: alexjlzheng@...il.com,
alexjlzheng@...cent.com,
chandan.babu@...cle.com,
linux-kernel@...r.kernel.org,
linux-xfs@...r.kernel.org,
david@...morbit.com
Subject: Re: [PATCH] xfs: make xfs_log_iovec independent from xfs_log_vec and release it early
On Mon, 24 Jun 2024 08:25:29 -0700, djwong@...nel.org wrote:
> 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.
xfs_log_iovec is where all log data is saved. Compared to xfs_log_vec itself,
xfs_log_iovec occupies a larger memory space.
When their memory spaces are allocated together, the memory occupied by
xfs_log_iovec can only be released after iclog is written to the disk log
space. But when xfs_log_iovec is written to iclog, its existence becomes
meaningless, because a copy of its content is already saved in iclog at this
time.
And if they are separated, we can release its memory when the data in
xfs_log_iovec is written to iclog. The interval between these two time points
is not too small.
Since xfs_log_iovec is the area that currently uses the most memory in
xfs_log_vec, this means that we have released quite a lot of memory. Freeing
memory that occupies a larger size earlier means smaller memory usage.
Jinliang Zheng
>
> --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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