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Message-ID: <4df4ef0c0801170347n7560c604l5a352791a73aa@mail.gmail.com>
Date: Thu, 17 Jan 2008 14:47:39 +0300
From: "Anton Salikhmetov" <salikhmetov@...il.com>
To: "Miklos Szeredi" <miklos@...redi.hu>
Cc: linux-mm@...ck.org, jakob@...hought.net,
linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
riel@...hat.com, ksm@...dk, staubach@...hat.com,
jesper.juhl@...il.com, torvalds@...ux-foundation.org,
a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
protasnb@...il.com, r.e.wolff@...wizard.nl,
hidave.darkstar@...il.com, hch@...radead.org
Subject: Re: [PATCH -v5 1/2] Massive code cleanup of sys_msync()
2008/1/17, Miklos Szeredi <miklos@...redi.hu>:
> > Substantial code cleanup of the sys_msync() function:
> >
> > 1) using the PAGE_ALIGN() macro instead of "manual" alignment;
> > 2) improved readability of the loop traversing the process memory regions.
> >
> > Signed-off-by: Anton Salikhmetov <salikhmetov@...il.com>
> > ---
> > mm/msync.c | 74 +++++++++++++++++++++++++++++------------------------------
> > 1 files changed, 36 insertions(+), 38 deletions(-)
> >
> > diff --git a/mm/msync.c b/mm/msync.c
> > index 144a757..44997bf 100644
> > --- a/mm/msync.c
> > +++ b/mm/msync.c
> > @@ -1,24 +1,22 @@
> > /*
> > - * linux/mm/msync.c
> > + * The msync() system call.
> > *
> > - * Copyright (C) 1994-1999 Linus Torvalds
> > + * Copyright (C) 1994-1999 Linus Torvalds
> > + * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@...il.com>
> > */
> >
> > -/*
> > - * The msync() system call.
> > - */
> > +#include <linux/file.h>
> > #include <linux/fs.h>
> > #include <linux/mm.h>
> > #include <linux/mman.h>
> > -#include <linux/file.h>
> > -#include <linux/syscalls.h>
> > #include <linux/sched.h>
> > +#include <linux/syscalls.h>
> >
> > /*
> > * MS_SYNC syncs the entire file - including mappings.
> > *
> > * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> > - * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
> > + * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
> > * Now it doesn't do anything, since dirty pages are properly tracked.
> > *
> > * The application may now run fsync() to
> > @@ -33,8 +31,7 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> > unsigned long end;
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma;
> > - int unmapped_error = 0;
> > - int error = -EINVAL;
> > + int error = -EINVAL, unmapped_error = 0;
>
> I prefer multi-line variable declarations, especially for ones with an
> initializer.
>
> >
> > if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
> > goto out;
> > @@ -42,62 +39,63 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> > goto out;
> > if ((flags & MS_ASYNC) && (flags & MS_SYNC))
> > goto out;
> > - error = -ENOMEM;
> > - len = (len + ~PAGE_MASK) & PAGE_MASK;
> > +
> > + len = PAGE_ALIGN(len);
> > end = start + len;
> > - if (end < start)
> > + if (end < start) {
> > + error = -ENOMEM;
>
> The usual style is to have the error assignment outside the
> conditional. That way is shorter, clearer, as well as possibly
> generating better code.
>
> > goto out;
> > + }
> > +
> > error = 0;
> > +
>
> Unnecessary empty line here, these two statements actually belong
> together.
>
> > if (end == start)
> > goto out;
> > +
> > /*
> > * If the interval [start,end) covers some unmapped address ranges,
> > * just ignore them, but return -ENOMEM at the end.
> > */
> > down_read(&mm->mmap_sem);
> > vma = find_vma(mm, start);
> > - for (;;) {
> > + do {
> > struct file *file;
> >
> > - /* Still start < end. */
> > - error = -ENOMEM;
> > - if (!vma)
> > - goto out_unlock;
> > - /* Here start < vma->vm_end. */
> > + if (!vma) {
> > + error = -ENOMEM;
> > + break;
> > + }
>
> Again, error asignment should be outside the conditional. This of
> course means, you'll have to set the error back to zero at the end of
> the loop, but that's fine.
>
> > if (start < vma->vm_start) {
> > start = vma->vm_start;
> > - if (start >= end)
> > - goto out_unlock;
> > + if (start >= end) {
> > + error = -ENOMEM;
> > + break;
> > + }
>
> Ditto.
>
> > unmapped_error = -ENOMEM;
> > }
> > - /* Here vma->vm_start <= start < vma->vm_end. */
> > - if ((flags & MS_INVALIDATE) &&
> > - (vma->vm_flags & VM_LOCKED)) {
> > + if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED)) {
> > error = -EBUSY;
>
> Ditto2.
>
> > - goto out_unlock;
> > + break;
> > }
> > - file = vma->vm_file;
> > start = vma->vm_end;
> > - if ((flags & MS_SYNC) && file &&
> > - (vma->vm_flags & VM_SHARED)) {
> > +
> > + file = vma->vm_file;
> > + if (file && (vma->vm_flags & VM_SHARED) && (flags & MS_SYNC)) {
> > get_file(file);
> > up_read(&mm->mmap_sem);
> > error = do_fsync(file, 0);
> > fput(file);
> > - if (error || start >= end)
> > + if (error)
>
> This simplifies, but also does unnecessary down/find_vma/up.
>
> > goto out;
> > down_read(&mm->mmap_sem);
> > vma = find_vma(mm, start);
> > - } else {
> > - if (start >= end) {
> > - error = 0;
> > - goto out_unlock;
> > - }
> > - vma = vma->vm_next;
> > + continue;
> > }
> > - }
> > -out_unlock:
> > +
> > + vma = vma->vm_next;
> > + } while (start < end);
> > up_read(&mm->mmap_sem);
> > +
> > out:
> > - return error ? : unmapped_error;
> > + return error ? error : unmapped_error;
> > }
>
Thanks for your recommendations!
I'll take them into account for the next version.
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