[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v3 3/7] support UFFD write fault processing in ram_save_itera

From: Andrey Gruzdev
Subject: Re: [PATCH v3 3/7] support UFFD write fault processing in ram_save_iterate()
Date: Fri, 20 Nov 2020 19:53:34 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 20.11.2020 19:43, Peter Xu wrote:
On Fri, Nov 20, 2020 at 07:15:07PM +0300, Andrey Gruzdev wrote:
Yeah, I think we can re-use the postcopy queue code for faulting pages. I'm
worring a little about some additional overhead dealing with urgent request
semaphore. Also, the code won't change a lot, something like:

         /* In case of 'write-tracking' migration we first try
          * to poll UFFD and sse if we have write page fault event */

         again = true;
         found = get_queued_page(rs, &pss);

         if (!found) {
             /* priority queue empty, so just search for something dirty */
             found = find_dirty_block(rs, &pss, &again);

Could I ask what's the "urgent request semaphore"?  Thanks,

These function use it (the correct name is 'rate_limit_sem'):

void migration_make_urgent_request(void)

void migration_consume_urgent_request(void)

They are called from ram_save_queue_pages and unqueue_page, accordingly, to control migration rate limiter.

bool migration_rate_limit(void)
         * Wait for a delay to do rate limiting OR
         * something urgent to post the semaphore.
        int ms = s->iteration_start_time + BUFFER_DELAY - now;
        if (qemu_sem_timedwait(&s->rate_limit_sem, ms) == 0) {
             * We were woken by one or more urgent things but
             * the timedwait will have consumed one of them.
             * The service routine for the urgent wake will dec
             * the semaphore itself for each item it consumes,
             * so add this one we just eat back.
            urgent = true;

Andrey Gruzdev, Principal Engineer
Virtuozzo GmbH  +7-903-247-6397

reply via email to

[Prev in Thread] Current Thread [Next in Thread]