[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] bitmap
From: |
Juan Quintela |
Subject: |
Re: [Qemu-devel] bitmap |
Date: |
Tue, 23 May 2017 13:24:26 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) |
Stefan Hajnoczi <address@hidden> wrote:
> On Mon, May 22, 2017 at 06:00:12PM +0430, ali saeedi wrote:
>> does this code 'atomic_rcu_read(&migration_bitmap_rcu)->bmap' return bitmap
>> of dirty blocks or bitmap of pages?
>
> This code changed recently. Please refer to qemu.git/master when asking
> questions on qemu-devel.
>
> I think you're asking about what is now RAMBlock->bmap. This bitmap
> describes pages (each page is TARGET_PAGE_SIZE bytes).
>
> This comment looks outdated, I don't think it returns a byte offset:
>
> /**
> * migration_bitmap_find_dirty: find the next dirty page from start
> *
> * Called with rcu_read_lock() to protect migration_bitmap
> *
> * Returns the byte offset within memory region of the start of a dirty page
> *
> * @rs: current RAM state
> * @rb: RAMBlock where to search for dirty pages
> * @start: page where we start the search
> */
> static inline
> unsigned long migration_bitmap_find_dirty(RAMState *rs, RAMBlock *rb,
> unsigned long start)
>
> Evidence:
>
> static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
> {
> pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
> ...
> if ((pss->page << TARGET_PAGE_BITS) >= pss->block->used_length) {
>
> Stefan
Oops, thanks you are right.
We used to have a global dirty bitmap. As far as I know, it has always
worked on pages. TARGET_PAGE_SIZE to be exact. Since 2.10 open out, we
moved to a bitmap by RAMBlock. It used to return an absolute page
number, now it returns a page number relative to the start of the block.
Later, Juan.