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Message-ID: <b4f557cb-c72b-44e6-b7dc-808005a47fda@huaweicloud.com>
Date: Mon, 1 Jul 2024 14:19:38 +0800
From: Baokun Li <libaokun@...weicloud.com>
To: linux-block@...r.kernel.org
Cc: axboe@...nel.dk, hch@...radead.org, linux-kernel@...r.kernel.org,
yangerkun@...wei.com, houtao1@...wei.com, yukuai3@...wei.com,
libaokun1@...wei.com
Subject: Re: [PATCH -next] blk-wbt: don't throttle swap writes in direct
reclaim
Friendly ping...
On 2024/6/4 11:05, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
>
> Now we avoid throttling swap writes by determining whether the current
> process is kswapd (aka current_is_kswapd()), but swap writes can come
> from either kswapd or direct reclaim, so the swap writes from direct
> reclaim will still be throttled.
>
> When a process holds a lock to allocate a free page, and enters direct
> reclaim because there is no free memory, then it might trigger a hung
> due to the wbt throttling that causes other processes to fail to get
> the lock.
>
> Both kswapd and direct reclaim set the REQ_SWAP flag, so use REQ_SWAP
> instead of current_is_kswapd() to avoid throttling swap writes. Also
> renamed WBT_KSWAPD to WBT_SWAP and WBT_RWQ_KSWAPD to WBT_RWQ_SWAP.
>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
> block/blk-wbt.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index 64472134dd26..aaacf2f5b223 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -37,7 +37,7 @@
> enum wbt_flags {
> WBT_TRACKED = 1, /* write, tracked for throttling */
> WBT_READ = 2, /* read */
> - WBT_KSWAPD = 4, /* write, from kswapd */
> + WBT_SWAP = 4, /* write, from swap_writepage() */
> WBT_DISCARD = 8, /* discard */
>
> WBT_NR_BITS = 4, /* number of bits */
> @@ -45,7 +45,7 @@ enum wbt_flags {
>
> enum {
> WBT_RWQ_BG = 0,
> - WBT_RWQ_KSWAPD,
> + WBT_RWQ_SWAP,
> WBT_RWQ_DISCARD,
> WBT_NUM_RWQ,
> };
> @@ -172,8 +172,8 @@ static bool wb_recent_wait(struct rq_wb *rwb)
> static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
> enum wbt_flags wb_acct)
> {
> - if (wb_acct & WBT_KSWAPD)
> - return &rwb->rq_wait[WBT_RWQ_KSWAPD];
> + if (wb_acct & WBT_SWAP)
> + return &rwb->rq_wait[WBT_RWQ_SWAP];
> else if (wb_acct & WBT_DISCARD)
> return &rwb->rq_wait[WBT_RWQ_DISCARD];
>
> @@ -528,7 +528,7 @@ static bool close_io(struct rq_wb *rwb)
> time_before(now, rwb->last_comp + HZ / 10);
> }
>
> -#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
> +#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO | REQ_SWAP)
>
> static inline unsigned int get_limit(struct rq_wb *rwb, blk_opf_t opf)
> {
> @@ -539,13 +539,13 @@ static inline unsigned int get_limit(struct rq_wb *rwb, blk_opf_t opf)
>
> /*
> * At this point we know it's a buffered write. If this is
> - * kswapd trying to free memory, or REQ_SYNC is set, then
> + * swap trying to free memory, or REQ_SYNC is set, then
> * it's WB_SYNC_ALL writeback, and we'll use the max limit for
> * that. If the write is marked as a background write, then use
> * the idle limit, or go to normal if we haven't had competing
> * IO for a bit.
> */
> - if ((opf & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
> + if ((opf & REQ_HIPRIO) || wb_recent_wait(rwb))
> limit = rwb->rq_depth.max_depth;
> else if ((opf & REQ_BACKGROUND) || close_io(rwb)) {
> /*
> @@ -622,8 +622,8 @@ static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
> if (bio_op(bio) == REQ_OP_READ) {
> flags = WBT_READ;
> } else if (wbt_should_throttle(bio)) {
> - if (current_is_kswapd())
> - flags |= WBT_KSWAPD;
> + if (bio->bi_opf & REQ_SWAP)
> + flags |= WBT_SWAP;
> if (bio_op(bio) == REQ_OP_DISCARD)
> flags |= WBT_DISCARD;
> flags |= WBT_TRACKED;
--
With Best Regards,
Baokun Li
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