| Message ID | 20171215220450.7899-4-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Dec 15, 2017 at 02:03:35PM -0800, Matthew Wilcox wrote: > From: Matthew Wilcox <mawilcox@microsoft.com> > > This results in no change in structure size on 64-bit x86 as it fits in > the padding between the gfp_t and the void *. The patch does more than described in the subject and commit message. At first I was confused why do you need to touch idr here. It took few minutes to figure it out. Could you please add more into commit message about lockname and xa_ locking interface since you introduce it here?
On Tue, Dec 26, 2017 at 07:54:40PM +0300, Kirill A. Shutemov wrote: > On Fri, Dec 15, 2017 at 02:03:35PM -0800, Matthew Wilcox wrote: > > From: Matthew Wilcox <mawilcox@microsoft.com> > > > > This results in no change in structure size on 64-bit x86 as it fits in > > the padding between the gfp_t and the void *. > > The patch does more than described in the subject and commit message. At first > I was confused why do you need to touch idr here. It took few minutes to figure > it out. > > Could you please add more into commit message about lockname and xa_ locking > interface since you introduce it here? Sure! How's this? xarray: Add the xa_lock to the radix_tree_root This results in no change in structure size on 64-bit x86 as it fits in the padding between the gfp_t and the void *. Initialising the spinlock requires a name for the benefit of lockdep, so RADIX_TREE_INIT() now needs to know the name of the radix tree it's initialising, and so do IDR_INIT() and IDA_INIT(). Also add the xa_lock() and xa_unlock() family of wrappers to make it easier to use the lock. If we could rely on -fplan9-extensions in the compiler, we could avoid all of this syntactic sugar, but that wasn't added until gcc 4.6. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote: > Also add the xa_lock() and xa_unlock() family of wrappers to make it > easier to use the lock. If we could rely on -fplan9-extensions in > the compiler, we could avoid all of this syntactic sugar, but that > wasn't added until gcc 4.6. Oh, in case anyone's wondering, here's how I'd do it with plan9 extensions: struct xarray { spinlock_t; int xa_flags; void *xa_head; }; ... spin_lock_irqsave(&mapping->pages, flags); __delete_from_page_cache(page, NULL); spin_unlock_irqrestore(&mapping->pages, flags); ... The plan9 extensions permit passing a pointer to a struct which has an unnamed element to a function which is expecting a pointer to the type of that element. The compiler does any necessary arithmetic to produce a pointer. It's exactly as if I had written: spin_lock_irqsave(&mapping->pages.xa_lock, flags); __delete_from_page_cache(page, NULL); spin_unlock_irqrestore(&mapping->pages.xa_lock, flags); More details here: https://9p.io/sys/doc/compiler.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote: > On Tue, Dec 26, 2017 at 07:54:40PM +0300, Kirill A. Shutemov wrote: > > On Fri, Dec 15, 2017 at 02:03:35PM -0800, Matthew Wilcox wrote: > > > From: Matthew Wilcox <mawilcox@microsoft.com> > > > > > > This results in no change in structure size on 64-bit x86 as it fits in > > > the padding between the gfp_t and the void *. > > > > The patch does more than described in the subject and commit message. At first > > I was confused why do you need to touch idr here. It took few minutes to figure > > it out. > > > > Could you please add more into commit message about lockname and xa_ locking > > interface since you introduce it here? > > Sure! How's this? > > xarray: Add the xa_lock to the radix_tree_root > > This results in no change in structure size on 64-bit x86 as it fits in > the padding between the gfp_t and the void *. > > Initialising the spinlock requires a name for the benefit of lockdep, > so RADIX_TREE_INIT() now needs to know the name of the radix tree it's > initialising, and so do IDR_INIT() and IDA_INIT(). > > Also add the xa_lock() and xa_unlock() family of wrappers to make it > easier to use the lock. If we could rely on -fplan9-extensions in > the compiler, we could avoid all of this syntactic sugar, but that > wasn't added until gcc 4.6. > Looks great, thanks.
On Tue, Dec 26, 2017 at 07:58:15PM -0800, Matthew Wilcox wrote: > On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote: > > Also add the xa_lock() and xa_unlock() family of wrappers to make it > > easier to use the lock. If we could rely on -fplan9-extensions in > > the compiler, we could avoid all of this syntactic sugar, but that > > wasn't added until gcc 4.6. > > Oh, in case anyone's wondering, here's how I'd do it with plan9 extensions: > > struct xarray { > spinlock_t; > int xa_flags; > void *xa_head; > }; > > ... > spin_lock_irqsave(&mapping->pages, flags); > __delete_from_page_cache(page, NULL); > spin_unlock_irqrestore(&mapping->pages, flags); > ... > > The plan9 extensions permit passing a pointer to a struct which has an > unnamed element to a function which is expecting a pointer to the type > of that element. The compiler does any necessary arithmetic to produce > a pointer. It's exactly as if I had written: > > spin_lock_irqsave(&mapping->pages.xa_lock, flags); > __delete_from_page_cache(page, NULL); > spin_unlock_irqrestore(&mapping->pages.xa_lock, flags); > > More details here: https://9p.io/sys/doc/compiler.html Yeah, that's neat. Dealing with old compilers is frustrating...
On Tue, Dec 26, 2017 at 07:58:15PM -0800, Matthew Wilcox wrote: > On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote: > > Also add the xa_lock() and xa_unlock() family of wrappers to make it > > easier to use the lock. If we could rely on -fplan9-extensions in > > the compiler, we could avoid all of this syntactic sugar, but that > > wasn't added until gcc 4.6. > > Oh, in case anyone's wondering, here's how I'd do it with plan9 extensions: > > struct xarray { > spinlock_t; > int xa_flags; > void *xa_head; > }; > > ... > spin_lock_irqsave(&mapping->pages, flags); > __delete_from_page_cache(page, NULL); > spin_unlock_irqrestore(&mapping->pages, flags); > ... > > The plan9 extensions permit passing a pointer to a struct which has an > unnamed element to a function which is expecting a pointer to the type > of that element. The compiler does any necessary arithmetic to produce > a pointer. It's exactly as if I had written: > > spin_lock_irqsave(&mapping->pages.xa_lock, flags); > __delete_from_page_cache(page, NULL); > spin_unlock_irqrestore(&mapping->pages.xa_lock, flags); > > More details here: https://9p.io/sys/doc/compiler.html I read the link, and I understand (from section 3.3) that replacing foo.bar.baz.goo with foo.goo is less typing, but otoh the first time I read your example above I thought "we're passing (an array of pages | something that doesn't have the word 'lock' in the name) to spin_lock_irqsave? wtf?" I suppose it does force me to go dig into whatever mapping->pages is to figure out that there's an unnamed spinlock_t and that the compiler can insert the appropriate pointer arithmetic, but now my brain trips over 'pages' being at the end of the selector for parameter 1 which slows down my review reading... OTOH I guess it /did/ motivate me to click the link, so well played, sir. :) --D > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jan 02, 2018 at 10:01:55AM -0800, Darrick J. Wong wrote: > On Tue, Dec 26, 2017 at 07:58:15PM -0800, Matthew Wilcox wrote: > > spin_lock_irqsave(&mapping->pages, flags); > > __delete_from_page_cache(page, NULL); > > spin_unlock_irqrestore(&mapping->pages, flags); > > > > More details here: https://9p.io/sys/doc/compiler.html > > I read the link, and I understand (from section 3.3) that replacing > foo.bar.baz.goo with foo.goo is less typing, but otoh the first time I > read your example above I thought "we're passing (an array of pages | > something that doesn't have the word 'lock' in the name) to > spin_lock_irqsave? wtf?" I can see that being a bit jarring initially. If you think about what object-oriented languages were offering in the nineties, this is basically C++ multiple-inheritance / Java interfaces. So when I read the above example, I think "lock the mapping pages, delete from page cache, unlock the mapping pages", and I don't have a wtf moment. It's just simpler to read than "lock the mapping pages lock", and less redundant. > I suppose it does force me to go dig into whatever mapping->pages is to > figure out that there's an unnamed spinlock_t and that the compiler can > insert the appropriate pointer arithmetic, but now my brain trips over > 'pages' being at the end of the selector for parameter 1 which slows > down my review reading... > > OTOH I guess it /did/ motivate me to click the link, so well played, > sir. :) Now if only I can trick you into giving your ACK on patch 1, "xfs: Rename xa_ elements to ail_" -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c index d844dcb80570..aac1e02f75df 100644 --- a/fs/f2fs/gc.c +++ b/fs/f2fs/gc.c @@ -991,7 +991,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, unsigned int init_segno = segno; struct gc_inode_list gc_list = { .ilist = LIST_HEAD_INIT(gc_list.ilist), - .iroot = RADIX_TREE_INIT(GFP_NOFS), + .iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS), }; trace_f2fs_gc_begin(sbi->sb, sync, background, diff --git a/include/linux/idr.h b/include/linux/idr.h index 8432bbfe02ce..45a77d32dcf6 100644 --- a/include/linux/idr.h +++ b/include/linux/idr.h @@ -31,11 +31,11 @@ struct idr { /* Set the IDR flag and the IDR_FREE tag */ #define IDR_RT_MARKER ((__force gfp_t)(3 << __GFP_BITS_SHIFT)) -#define IDR_INIT \ +#define IDR_INIT(name) \ { \ - .idr_rt = RADIX_TREE_INIT(IDR_RT_MARKER) \ + .idr_rt = RADIX_TREE_INIT(name, IDR_RT_MARKER) \ } -#define DEFINE_IDR(name) struct idr name = IDR_INIT +#define DEFINE_IDR(name) struct idr name = IDR_INIT(name) /** * idr_get_cursor - Return the current position of the cyclic allocator @@ -194,10 +194,10 @@ struct ida { struct radix_tree_root ida_rt; }; -#define IDA_INIT { \ - .ida_rt = RADIX_TREE_INIT(IDR_RT_MARKER | GFP_NOWAIT), \ +#define IDA_INIT(name) { \ + .ida_rt = RADIX_TREE_INIT(name, IDR_RT_MARKER | GFP_NOWAIT), \ } -#define DEFINE_IDA(name) struct ida name = IDA_INIT +#define DEFINE_IDA(name) struct ida name = IDA_INIT(name) int ida_pre_get(struct ida *ida, gfp_t gfp_mask); int ida_get_new_above(struct ida *ida, int starting_id, int *p_id); diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index fc55ff31eca7..d2253b540cd7 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -109,20 +109,23 @@ struct radix_tree_node { #define ROOT_TAG_SHIFT (__GFP_BITS_SHIFT + 1) struct radix_tree_root { + spinlock_t xa_lock; gfp_t gfp_mask; struct radix_tree_node __rcu *rnode; }; -#define RADIX_TREE_INIT(mask) { \ +#define RADIX_TREE_INIT(name, mask) { \ + .xa_lock = __SPIN_LOCK_UNLOCKED(name.xa_lock), \ .gfp_mask = (mask), \ .rnode = NULL, \ } #define RADIX_TREE(name, mask) \ - struct radix_tree_root name = RADIX_TREE_INIT(mask) + struct radix_tree_root name = RADIX_TREE_INIT(name, mask) #define INIT_RADIX_TREE(root, mask) \ do { \ + spin_lock_init(&(root)->xa_lock); \ (root)->gfp_mask = (mask); \ (root)->rnode = NULL; \ } while (0) diff --git a/include/linux/xarray.h b/include/linux/xarray.h new file mode 100644 index 000000000000..931a0ff61315 --- /dev/null +++ b/include/linux/xarray.h @@ -0,0 +1,33 @@ +#ifndef _LINUX_XARRAY_H +#define _LINUX_XARRAY_H +/* + * eXtensible Arrays + * Copyright (c) 2017 Microsoft Corporation + * Author: Matthew Wilcox <mawilcox@microsoft.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of + * the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +#include <linux/spinlock.h> + +#define xa_trylock(xa) spin_trylock(&(xa)->xa_lock) +#define xa_lock(xa) spin_lock(&(xa)->xa_lock) +#define xa_unlock(xa) spin_unlock(&(xa)->xa_lock) +#define xa_lock_bh(xa) spin_lock_bh(&(xa)->xa_lock) +#define xa_unlock_bh(xa) spin_unlock_bh(&(xa)->xa_lock) +#define xa_lock_irq(xa) spin_lock_irq(&(xa)->xa_lock) +#define xa_unlock_irq(xa) spin_unlock_irq(&(xa)->xa_lock) +#define xa_lock_irqsave(xa, flags) \ + spin_lock_irqsave(&(xa)->xa_lock, flags) +#define xa_unlock_irqrestore(xa, flags) \ + spin_unlock_irqrestore(&(xa)->xa_lock, flags) + +#endif /* _LINUX_XARRAY_H */ diff --git a/kernel/pid.c b/kernel/pid.c index b13b624e2c49..b050b4643eee 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -58,7 +58,7 @@ int pid_max_max = PID_MAX_LIMIT; */ struct pid_namespace init_pid_ns = { .kref = KREF_INIT(2), - .idr = IDR_INIT, + .idr = IDR_INIT(init_pid_ns.idr), .pid_allocated = PIDNS_ADDING, .level = 0, .child_reaper = &init_task, diff --git a/tools/include/linux/spinlock.h b/tools/include/linux/spinlock.h index 4ed569fcb139..b21b586b9854 100644 --- a/tools/include/linux/spinlock.h +++ b/tools/include/linux/spinlock.h @@ -7,6 +7,7 @@ #define spinlock_t pthread_mutex_t #define DEFINE_SPINLOCK(x) pthread_mutex_t x = PTHREAD_MUTEX_INITIALIZER; +#define __SPIN_LOCK_UNLOCKED(x) (pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER #define spin_lock_irqsave(x, f) (void)f, pthread_mutex_lock(x) #define spin_unlock_irqrestore(x, f) (void)f, pthread_mutex_unlock(x)