The patch titled Subject: pagemap: prepare to reuse constant bits with page-shift has been added to the -mm tree. Its filename is pagemap-prepare-to-reuse-constant-bits-with-page-shift.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Subject: pagemap: prepare to reuse constant bits with page-shift In order to reuse bits from pagemap entries gracefully, we leave the entries as is but on pagemap open emit a warning in dmesg, that bits 55-60 are about to change in a couple of releases. Next, if a user issues soft-dirty clear command via the clear_refs file (it was disabled before v3.9) we assume that he's aware of the new pagemap format, note that fact and report the bits in pagemap in the new manner. The "migration strategy" looks like this then: 1. existing users are not affected -- they don't touch soft-dirty feature, thus see old bits in pagemap, but are warned and have time to fix themselves 2. those who use soft-dirty know about new pagemap format 3. some time soon we get rid of any signs of page-shift in pagemap as well as this trick with clear-soft-dirty affecting pagemap format. Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Cc: Matt Mackall <mpm@xxxxxxxxxxx> Cc: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> Cc: Glauber Costa <glommer@xxxxxxxxxxxxx> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/vm/pagemap.txt | 3 +- fs/proc/task_mmu.c | 35 ++++++++++++++++++++++++++++++++- 2 files changed, 36 insertions(+), 2 deletions(-) diff -puN Documentation/vm/pagemap.txt~pagemap-prepare-to-reuse-constant-bits-with-page-shitf Documentation/vm/pagemap.txt --- a/Documentation/vm/pagemap.txt~pagemap-prepare-to-reuse-constant-bits-with-page-shitf +++ a/Documentation/vm/pagemap.txt @@ -15,7 +15,8 @@ There are three components to pagemap: * Bits 0-54 page frame number (PFN) if present * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped - * Bits 55-60 page shift (page size = 1<<page shift) + * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) + * Bits 56-60 zero * Bit 61 page is file-page or shared-anon * Bit 62 page swapped * Bit 63 page present diff -puN fs/proc/task_mmu.c~pagemap-prepare-to-reuse-constant-bits-with-page-shitf fs/proc/task_mmu.c --- a/fs/proc/task_mmu.c~pagemap-prepare-to-reuse-constant-bits-with-page-shitf +++ a/fs/proc/task_mmu.c @@ -688,6 +688,23 @@ const struct file_operations proc_tid_sm .release = seq_release_private, }; +/* + * We do not want to have constant page-shift bits sitting in + * pagemap entries and are about to reuse them some time soon. + * + * Here's the "migration strategy": + * 1. when the system boots these bits remain what they are, + * but a warning about future change is printed in log; + * 2. once anyone clears soft-dirty bits via clear_refs file, + * these flag is set to denote, that user is aware of the + * new API and those page-shift bits change their meaning. + * The respective warning is printed in dmesg; + * 3. In a couple of releases we will remove all the mentions + * of page-shift in pagemap entries. + */ + +static bool soft_dirty_cleared __read_mostly; + enum clear_refs_types { CLEAR_REFS_ALL = 1, CLEAR_REFS_ANON, @@ -777,6 +794,13 @@ static ssize_t clear_refs_write(struct f type = (enum clear_refs_types)itype; if (type < CLEAR_REFS_ALL || type >= CLEAR_REFS_LAST) return -EINVAL; + + if (type == CLEAR_REFS_SOFT_DIRTY) { + soft_dirty_cleared = true; + pr_warn_once("The pagemap bits 55-60 has changed their meaning! " + "See the linux/Documentation/vm/pagemap.txt for details.\n"); + } + task = get_proc_task(file_inode(file)); if (!task) return -ESRCH; @@ -1086,7 +1110,7 @@ static ssize_t pagemap_read(struct file if (!count) goto out_task; - pm.v2 = false; + pm.v2 = soft_dirty_cleared; pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT); pm.buffer = kmalloc(pm.len, GFP_TEMPORARY); ret = -ENOMEM; @@ -1159,9 +1183,18 @@ out: return ret; } +static int pagemap_open(struct inode *inode, struct file *file) +{ + pr_warn_once("Bits 55-60 of /proc/PID/pagemap entries are about " + "to stop being page-shift some time soon. See the " + "linux/Documentation/vm/pagemap.txt for details.\n"); + return 0; +} + const struct file_operations proc_pagemap_operations = { .llseek = mem_lseek, /* borrow this */ .read = pagemap_read, + .open = pagemap_open, }; #endif /* CONFIG_PROC_PAGE_MONITOR */ _ Patches currently in -mm which might be from xemul@xxxxxxxxxxxxx are origin.patch clear_refs-sanitize-accepted-commands-declaration.patch clear_refs-introduce-private-struct-for-mm_walk.patch pagemap-introduce-pagemap_entry_t-without-pmshift-bits.patch pagemap-introduce-pagemap_entry_t-without-pmshift-bits-v4.patch mm-soft-dirty-bits-for-user-memory-changes-tracking.patch pagemap-prepare-to-reuse-constant-bits-with-page-shift.patch linux-next.patch selftest-add-simple-test-for-soft-dirty-bit.patch ptrace-add-ability-to-retrieve-signals-without-removing-from-a-queue-v4.patch selftest-add-a-test-case-for-ptrace_peeksiginfo.patch kernel-sysc-make-prctlpr_set_mm-generally-available.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html