Re: [Qemu-devel] [PATCH 6/6] Don't abort on memory allocation error

[Orit Wasserman]

On 01/30/2014 06:08 PM, Dr. David Alan Gilbert wrote:
> * Orit Wasserman (address@hidden) wrote:
> > It is better to fail migration in case of failure to
> > allocate new cache item
>
> Does this actually fail migration or just drop back to sending an uncompressed
> page? (I think the latter, and that's an even better result).

It fails the migration, if the users wants to disable compression it can do it
and start migration again.

> > Signed-off-by: Orit Wasserman <address@hidden>
> > ---
> >   arch_init.c                    |  4 +++-
> >   include/migration/page_cache.h |  4 +++-
> >   page_cache.c                   | 16 +++++++++++-----
> >   3 files changed, 17 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch_init.c b/arch_init.c
> > index 806d096..0bfbc5a 100644
> > --- a/arch_init.c
> > +++ b/arch_init.c
> > @@ -284,7 +284,9 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t 
> > *current_data,
> >
> >       if (!cache_is_cached(XBZRLE.cache, current_addr)) {
> >           if (!last_stage) {
> > -            cache_insert(XBZRLE.cache, current_addr, current_data);
> > +            if (cache_insert(XBZRLE.cache, current_addr, current_data) == -1) {
> > +                return -1;
> > +            }
> >           }
> >           acct_info.xbzrle_cache_miss++;
> >           return -1;
> > diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h
> > index 87894fe..d156f0d 100644
> > --- a/include/migration/page_cache.h
> > +++ b/include/migration/page_cache.h
> > @@ -60,11 +60,13 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t 
> > addr);
> >    * cache_insert: insert the page into the cache. the page cache
> >    * will dup the data on insert. the previous value will be overwritten
> >    *
> > + * Returns -1 on error
> > + *
> >    * @cache pointer to the PageCache struct
> >    * @addr: page address
> >    * @pdata: pointer to the page
> >    */
> > -void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata);
> > +int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata);
> >
> >   /**
> >    * cache_resize: resize the page cache. In case of size reduction the extra
> > diff --git a/page_cache.c b/page_cache.c
> > index 62a53f8..69e8329 100644
> > --- a/page_cache.c
> > +++ b/page_cache.c
> > @@ -150,7 +150,7 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t 
> > addr)
> >       return cache_get_by_addr(cache, addr)->it_data;
> >   }
> >
> > -void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
> > +int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
> >   {
> >
> >       CacheItem *it = NULL;
> > @@ -161,16 +161,22 @@ void cache_insert(PageCache *cache, uint64_t addr, 
> > uint8_t *pdata)
> >       /* actual update of entry */
> >       it = cache_get_by_addr(cache, addr);
> >
> > -    /* free old cached data if any */
> > -    g_free(it->it_data);
> > -
> > +    /* allocate page */
> >       if (!it->it_data) {
> >           cache->num_items++;
> > +        it->it_data = g_try_malloc(cache->page_size);
> > +        if (!it->it_data) {
> > +            DPRINTF("Error allocating page\n");
> > +            return -1;
> > +        }
>
> It feels like it would have been correct to do the num_items++ after the
> allocation test (although since the num_items doesn't seem to be used
> anywhere that's not a show-stopper, but worth fixing sometime).

You are correct, I will move it after allocation.

Orit
> >       }
> >
> > -    it->it_data = g_memdup(pdata, cache->page_size);
> > +    memcpy(it->it_data, pdata, cache->page_size);
> > +
> >       it->it_age = ++cache->max_item_age;
> >       it->it_addr = addr;
> > +
> > +    return 0;
> >   }
> >
> >   int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
> > --
> > 1.8.3.1
>
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>
>
> Dave
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK