Messages in this thread | | | Date | Mon, 11 Dec 2006 09:13:11 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [BUG] commit 3c517a61, slab: better fallback allocation behavior |
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On Sun, 10 Dec 2006, Andrew Morton wrote:
> > I fixed the cpuset_zone_allowed() call from fallback_alloc() to avoid > > sleeping. Notice the __GFP_HARDWALL added in Linus's version, or the > > new function cpuset_zone_allowed_hardwall() in Andrew's version, all > > done in the last week. > > > > But apparently kmem_getpages() can also sleep, as it calls __alloc_pages().
Yes fallback_alloc calls kmem_getpages() and if one does not set the gfp flags properly __alloc_pages will sleep. fallback_alloc() uses the passed flags so if kmem_cache_alloc is called with the proper flags set then __alloc_pages() will not sleep.
In this case kmem_cache_alloc() is called from journal_alloc_journal_head() with GFP_NOFS set which is
#define GFP_NOFS (__GFP_WAIT | __GFP_IO)
__GFP_WAIT means
#define __GFP_WAIT ((__force gfp_t)0x10u) /* Can wait and reschedule? */
Thus the caller allows __alloc_pages to sleep.
/* * journal_head splicing and dicing */ static struct journal_head *journal_alloc_journal_head(void) { struct journal_head *ret; static unsigned long last_warning;
#ifdef CONFIG_JBD_DEBUG atomic_inc(&nr_journal_heads); #endif ret = kmem_cache_alloc(journal_head_cache, GFP_NOFS); if (ret == 0) { jbd_debug(1, "out of memory for journal_head\n"); if (time_after(jiffies, last_warning + 5*HZ)) { printk(KERN_NOTICE "ENOMEM in %s, retrying.\n", __FUNCTION__); last_warning = jiffies; } while (ret == 0) { yield(); ret = kmem_cache_alloc(journal_head_cache, GFP_NOFS); } } return ret; }
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