Messages in this thread Patch in this message | | | Subject | [PATCH] remove throttle_vm_writeout() | From | Miklos Szeredi <> | Date | Thu, 04 Oct 2007 14:25:22 +0200 |
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This in preparation for the writable mmap patches for fuse. I know it conflicts with
writeback-remove-unnecessary-wait-in-throttle_vm_writeout.patch
but if this function is to be removed, it doesn't make much sense to fix it first ;) ---
From: Miklos Szeredi <mszeredi@suse.cz>
By relying on the global diry limits, this can cause a deadlock when devices are stacked.
If the stacking is done through a fuse filesystem, the __GFP_FS, __GFP_IO tests won't help: the process doing the allocation doesn't have any special flag.
So why exactly does this function exist?
Direct reclaim does not _increase_ the number of dirty pages in the system, so rate limiting it seems somewhat pointless.
There are two cases:
1) File backed pages -> file
dirty + writeback count remains constant
2) Anonymous pages -> swap
writeback count increases, dirty balancing will hold back file writeback in favor of swap
So the real question is: does case 2 need rate limiting, or is it OK to let the device queue fill with swap pages as fast as possible?
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> ---
Index: linux/include/linux/writeback.h =================================================================== --- linux.orig/include/linux/writeback.h 2007-10-02 16:55:03.000000000 +0200 +++ linux/include/linux/writeback.h 2007-10-04 13:40:33.000000000 +0200 @@ -94,7 +94,6 @@ static inline void inode_sync_wait(struc int wakeup_pdflush(long nr_pages); void laptop_io_completion(void); void laptop_sync_completion(void); -void throttle_vm_writeout(gfp_t gfp_mask); /* These are exported to sysctl. */ extern int dirty_background_ratio; Index: linux/mm/page-writeback.c =================================================================== --- linux.orig/mm/page-writeback.c 2007-10-02 16:55:03.000000000 +0200 +++ linux/mm/page-writeback.c 2007-10-04 13:40:33.000000000 +0200 @@ -497,37 +497,6 @@ void balance_dirty_pages_ratelimited_nr( } EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); -void throttle_vm_writeout(gfp_t gfp_mask) -{ - long background_thresh; - long dirty_thresh; - - if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) { - /* - * The caller might hold locks which can prevent IO completion - * or progress in the filesystem. So we cannot just sit here - * waiting for IO to complete. - */ - congestion_wait(WRITE, HZ/10); - return; - } - - for ( ; ; ) { - get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); - - /* - * Boost the allowable dirty threshold a bit for page - * allocators so they don't get DoS'ed by heavy writers - */ - dirty_thresh += dirty_thresh / 10; /* wheeee... */ - - if (global_page_state(NR_UNSTABLE_NFS) + - global_page_state(NR_WRITEBACK) <= dirty_thresh) - break; - congestion_wait(WRITE, HZ/10); - } -} - /* * writeback at least _min_pages, and keep writing until the amount of dirty * memory is less than the background threshold, or until we're all clean. Index: linux/mm/vmscan.c =================================================================== --- linux.orig/mm/vmscan.c 2007-10-02 16:55:03.000000000 +0200 +++ linux/mm/vmscan.c 2007-10-04 13:40:33.000000000 +0200 @@ -1184,7 +1184,6 @@ static unsigned long shrink_zone(int pri } } - throttle_vm_writeout(sc->gfp_mask); return nr_reclaimed; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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