Re: [PATCH v5 1/2] mm: Add become_kswapd and restore_kswapd
From: Matthew Wilcox <willy@infradead.org>
Date: 2020-08-19 03:09:05
Also in:
linux-fsdevel, linux-xfs
On Wed, Aug 19, 2020 at 10:24:24AM +0800, Yafang Shao wrote:
From: "Matthew Wilcox (Oracle)" <willy@infradead.org> Since XFS needs to pretend to be kswapd in some of its worker threads, create methods to save & restore kswapd state. Don't bother restoring kswapd state in kswapd -- the only time we reach this code is when we're exiting and the task_struct is about to be destroyed anyway. Cc: Dave Chinner <david@fromorbit.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Darrick J. Wong <redacted> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Yafang Shao <redacted>
See https://lore.kernel.org/linux-mm/20200625123143.GK1320@dhcp22.suse.cz/ (local) Please add: Acked-by: Michal Hocko <mhocko@suse.com>
+/* + * Tell the memory management that we're a "memory allocator", + * and that if we need more memory we should get access to it + * regardless (see "__alloc_pages()"). "kswapd" should + * never get caught in the normal page freeing logic. + * + * (Kswapd normally doesn't need memory anyway, but sometimes + * you need a small amount of memory in order to be able to + * page out something else, and this flag essentially protects + * us from recursively trying to free more memory as we're + * trying to free the first piece of memory in the first place). + */
And let's change that comment as suggested by Michal (slightly edited by me): /* * Tell the memory management code that this thread is working on behalf * of background memory reclaim (like kswapd). That means that it will * get access to memory reserves should it need to allocate memory in * order to make forward progress. With this great power comes great * responsibility to not exhaust those reserves. */
quoted hunk ↗ jump to hunk
+#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) + +static inline unsigned long become_kswapd(void) +{ + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; + + current->flags |= KSWAPD_PF_FLAGS; + + return flags; +} + +static inline void restore_kswapd(unsigned long flags) +{ + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); +} + #ifdef CONFIG_MEMCG /** * memalloc_use_memcg - Starts the remote memcg charging scope.diff --git a/mm/vmscan.c b/mm/vmscan.c index 99e1796eb833..3a2615bfde35 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c@@ -3859,19 +3859,7 @@ static int kswapd(void *p) if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); - /* - * Tell the memory management that we're a "memory allocator", - * and that if we need more memory we should get access to it - * regardless (see "__alloc_pages()"). "kswapd" should - * never get caught in the normal page freeing logic. - * - * (Kswapd normally doesn't need memory anyway, but sometimes - * you need a small amount of memory in order to be able to - * page out something else, and this flag essentially protects - * us from recursively trying to free more memory as we're - * trying to free the first piece of memory in the first place). - */ - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; + become_kswapd(); set_freezable(); WRITE_ONCE(pgdat->kswapd_order, 0);@@ -3921,8 +3909,6 @@ static int kswapd(void *p) goto kswapd_try_sleep; } - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); - return 0; }-- 2.18.1