linux-kernel - Re: [PATCH v3 04/13] ltp/fsx.c: Add atomic writes support to fsx

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Message-ID: <20250723145733.GP2672039@frogsfrogsfrogs>
Date: Wed, 23 Jul 2025 07:57:33 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: Zorro Lang <zlang@...hat.com>, fstests@...r.kernel.org,
	Ritesh Harjani <ritesh.list@...il.com>, john.g.garry@...cle.com,
	tytso@....edu, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 04/13] ltp/fsx.c: Add atomic writes support to fsx

On Tue, Jul 22, 2025 at 03:29:02PM +0530, Ojaswin Mujoo wrote:
> On Thu, Jul 17, 2025 at 09:17:47AM -0700, Darrick J. Wong wrote:
> 
> <snip>
> 
> > > +
> > > +/*
> > > + * Round down n to nearest power of 2.
> > > + * If n is already a power of 2, return n;
> > > + */
> > > +static int rounddown_pow_of_2(int n) {
> > > +	int i = 0;
> > > +
> > > +	if (is_power_of_2(n))
> > > +		return n;
> > > +
> > > +	for (; (1 << i) < n; i++);
> > > +
> > > +	return 1 << (i - 1);
> > > +}
> > > +
> > >  void
> > >  dowrite(unsigned offset, unsigned size, int flags)
> > >  {
> > > @@ -1081,6 +1113,27 @@ dowrite(unsigned offset, unsigned size, int flags)
> > >  	offset -= offset % writebdy;
> > >  	if (o_direct)
> > >  		size -= size % writebdy;
> > > +	if (flags & RWF_ATOMIC) {
> > > +		/* atomic write len must be inbetween awu_min and awu_max */
> > > +		if (size < awu_min)
> > > +			size = awu_min;
> > > +		if (size > awu_max)
> > > +			size = awu_max;
> > > +
> > > +		/* atomic writes need power-of-2 sizes */
> > > +		size = rounddown_pow_of_2(size);
> > > +
> > > +		/* atomic writes need naturally aligned offsets */
> > > +		offset -= offset % size;
> > 
> > I don't think you should be modifying offset/size here.  Normally for
> > fsx we do all the rounding of the file range in the switch statement
> > after the "calculate appropriate op to run" comment statement.
> > 
> > --D
> 
> Yes, I noticed that but then I saw we make size/offset adjustments in
> do write for writebdy and I wanted atomic writes adjustments to be done
> after that.

<nod> ok then, I forgot that we already tweak the file range for
write...
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

--D


> Regads,
> ojaswin
> 
> > 
> > > +
> > > +		/* Skip the write if we are crossing max filesize */
> > > +		if ((offset + size) > maxfilelen) {
> > > +			if (!quiet && testcalls > simulatedopcount)
> > > +				prt("skipping atomic write past maxfilelen\n");
> > > +			log4(OP_WRITE_ATOMIC, offset, size, FL_SKIPPED);
> > > +			return;
> > > +		}
> > > +	}
> > >  	if (size == 0) {
> > >  		if (!quiet && testcalls > simulatedopcount && !o_direct)
> > >  			prt("skipping zero size write\n");
> > > @@ -1088,7 +1141,10 @@ dowrite(unsigned offset, unsigned size, int flags)
> > >  		return;
> > >  	}
> > >  
> > > -	log4(OP_WRITE, offset, size, FL_NONE);
> > > +	if (flags & RWF_ATOMIC)
> > > +		log4(OP_WRITE_ATOMIC, offset, size, FL_NONE);
> > > +	else
> > > +		log4(OP_WRITE, offset, size, FL_NONE);
> > >  
> > >  	gendata(original_buf, good_buf, offset, size);
> > >  	if (offset + size > file_size) {
> > > @@ -1108,8 +1164,9 @@ dowrite(unsigned offset, unsigned size, int flags)
> > >  		       (monitorstart == -1 ||
> > >  			(offset + size > monitorstart &&
> > >  			(monitorend == -1 || offset <= monitorend))))))
> > > -		prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d\n", testcalls,
> > > -		    offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0);
> > > +		prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d atomic_wr=%d\n", testcalls,
> > > +		    offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0,
> > > +		    (flags & RWF_ATOMIC) != 0);
> > >  	iret = fsxwrite(fd, good_buf + offset, size, offset, flags);
> > >  	if (iret != size) {
> > >  		if (iret == -1)
> > > @@ -1785,6 +1842,30 @@ do_dedupe_range(unsigned offset, unsigned length, unsigned dest)
> > >  }
> > >  #endif
> > >  
> > > +int test_atomic_writes(void) {
> > > +	int ret;
> > > +	struct statx stx;
> > > +
>